Adult Stem Cell Activity Research Articles

Appreciating animal induced pluripotent stem cells to shape plant cell reprogramming strategies.

Animals and plants have developed resilience mechanisms to effectively endure and overcome physical damage and environmental challenges throughout their life span. To sustain their vitality, both animals and plants employ mechanisms to replenish damaged cells, either directly, involving the activity of adult stem cells, or indirectly, via dedifferentiation of somatic cells that are induced to revert to a stem cell state and subsequently redifferentiate. Stem cell research has been a rapidly advancing field in animal studies for many years, driven by its promising potential in human therapeutics, including tissue regeneration and drug development. A major breakthrough was the discovery of induced pluripotent stem cells (iPSCs), which are reprogrammed from somatic cells by expressing a limited set of transcription factors. This discovery enabled the generation of an unlimited supply of cells that can be differentiated into specific cell types and tissues. Equally, a keen interest in the connection between plant stem cells and regeneration has been developed in the last decade, driven by the demand to enhance plant traits such as yield, resistance to pathogens, and the opportunities provided by CRISPR/Cas-mediated gene editing. Here we discuss how knowledge of stem cell biology benefits regeneration technology, and we speculate on the creation of a universal genotype-independent iPSC system for plants to overcome regenerative recalcitrance.

Serine and Arginine-Rich Splicing Factor 3 Promotes the Activation of Quiescent Mouse Neural Stem Cells.

The quiescence and activation of adult stem cells are regulated by many kinds of molecular mechanisms, and RNA alternative splicing participates in regulating many cellular processes. However, the relationship between stem cell quiescence and activation regulation and gene alternative splicing has yet to be studied. In this study, we aimed to elucidate the regulation of stem cell quiescence and activation by RNA alternative splicing. The upregulated genes in activated mouse neural stem cells (NSCs), muscle stem cells, and hematopoietic stem cells were collected for Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. The genes from three tissue stem cells underwent Venn analysis. The mouse NSCs were used for quiescence and reactivation induction. The immunostaining of cell-specific markers was performed to identify cell properties. The reverse transcription-polymerase chain reaction and western blotting were used to detect the gene expression and protein expression, respectively. We found that the upregulated genes in activated stem cells from three tissues were all enriched in RNA splicing-related biological processes; the upregulated RNA splicing-related genes in activated stem cells displayed tissue differences; mouse NSCs were successfully induced into quiescence and reactivation in vitro without losing differentiation potential; serine and arginine-rich splicing factor 3 (Srsf3) was highly expressed in the activated mouse NSCs, and the overexpression of SRSF3 protein promoted the activation of quiescent mouse NSCs and increased the neural cell production. Our data indicate that the alternative splicing change may underline the transition of quiescence and activation of stem cells. The manipulation of the splicing factor may benefit tissue repair by promoting the activation of quiescent stem cells.

Adult stem cell activity in naked mole rats for long-term tissue maintenance

The naked mole rat (NMR), Heterocephalus glaber, the longest-living rodent, provides a unique opportunity to explore how evolution has shaped adult stem cell (ASC) activity and tissue function with increasing lifespan. Using cumulative BrdU labelling and a quantitative imaging approach to track intestinal ASCs (Lgr5+) in their native in vivo state, we find an expanded pool of Lgr5+ cells in NMRs, and these cells specifically at the crypt base (Lgr5+CBC) exhibit slower division rates compared to those in short-lived mice but have a similar turnover as human LGR5+CBC cells. Instead of entering quiescence (G0), NMR Lgr5+CBC cells reduce their division rates by prolonging arrest in the G1 and/or G2 phases of the cell cycle. Moreover, we also observe a higher proportion of differentiated cells in NMRs that confer enhanced protection and function to the intestinal mucosa which is able to detect any chemical imbalance in the luminal environment efficiently, triggering a robust pro-apoptotic, anti-proliferative response within the stem/progenitor cell zone.

Apoptosis is a generator of Wnt-dependent regeneration and homeostatic cell renewal in the ascidian Ciona.

ABSTRACTIn the ascidian Ciona intestinalis, basal body parts regenerate distal structures but distal body parts do not replace basal structures. Regeneration involves the activity of adult stem cells in the branchial sac, which proliferate and produce migratory progenitor cells for tissue and organ replacement. Branchial sac-derived stem cells also replenish recycling cells lining the pharyngeal fissures during homeostatic growth. Apoptosis at injury sites occurs early during regeneration and continuously in the pharyngeal fissures during homeostatic growth. Caspase 1 inhibitor, caspase 3 inhibitor, or pan-caspase inhibitor Z-VAD-FMK treatment blocked apoptosis, prevented regeneration, and suppressed branchial sac growth and function. A pharmacological screen and siRNA-mediated gene knockdown indicated that regeneration requires canonical Wnt signaling. Wnt3a protein rescued both caspase-blocked regeneration and branchial sac growth. Inhibition of apoptosis did not affect branchial sac stem cell proliferation but prevented the survival of progenitor cells. After bisection across the mid-body, apoptosis occurred only in the regenerating basal fragments, although both fragments contained a part of the branchial sac, suggesting that apoptosis is unilateral at the wound site and the presence of branchial sac stem cells is insufficient for regeneration. The results suggest that apoptosis-dependent Wnt signaling mediates regeneration and homeostatic growth in Ciona.

The DEAD-box helicase DDX56 is a conserved stemness regulator in normal and cancer stem cells

Across the animal kingdom, adult tissue homeostasis is regulated by adult stem cell activity, which is commonly dysregulated in human cancers. However, identifying key regulators of stem cells in the milieu of thousands of genes dysregulated in a given cancer is challenging. Here, using a comparative genomics approach between planarian adult stem cells and patient-derived glioblastoma stem cells (GSCs), we identify and demonstrate the role of DEAD-box helicase DDX56 in regulating aspects of stemness in four stem cell systems: planarians, mouse neural stem cells, human GSCs, and a fly model of glioblastoma. In a human GSC line, DDX56 localizes to the nucleolus, and using planarians, when DDX56 is lost, stem cells dysregulate expression of ribosomal RNAs and lose nucleolar integrity prior to stem cell death. Together, a comparative genomic approach can be used to uncover conserved stemness regulators that are functional in both normal and cancer stem cells.

Exogenous L-arginine increases intestinal stem cell function through CD90+ stromal cells producing mTORC1-induced Wnt2b

The renewal and repair of intestinal epithelium depend on the self-renewal of intestinal stem cells (ISCs) under physiological and pathological conditions. Although previous work has established that exogenous nutrients regulate adult stem cell activity, little is known about the regulatory effect of L-arginine on ISCs. In this study we utilize mice and small intestinal (SI) organoid models to clarify the role of L-arginine on epithelial differentiation of ISCs. We show that L-arginine increases expansion of ISCs in mice. Furthermore, CD90+ intestinal stromal cells augment stem-cell function in response to L-arginine in co-culture experiments. Mechanistically, we find that L-arginine stimulates Wnt2b secretion by CD90+ stromal cells through the mammalian target of rapamycin complex 1 (mTORC1) and that blocking Wnt2b production prevents L-arginine-induced ISC expansion. Finally, we show that L-arginine treatment protects the gut in response to injury. Our findings highlight an important role for CD90+ stromal cells in L-arginine-stimulated ISC expansion.

Notch and EGFR regulate apoptosis in progenitor cells to ensure gut homeostasis in Drosophila

The regenerative activity of adult stem cells carries a risk of cancer, particularly in highly renewable tissues. Members of the family of inhibitor of apoptosis proteins (IAPs) inhibit caspases and cell death, and are often deregulated in adult cancers; however, their roles in normal adult tissue homeostasis are unclear. Here, we show that regulation of the number of enterocyte‐committed progenitor (enteroblast) cells in the adult Drosophila involves a caspase‐mediated physiological apoptosis, which adaptively eliminates excess enteroblast cells produced by intestinal stem cells (ISCs) and, when blocked, can also lead to tumorigenesis. Importantly, we found that Diap1 is expressed by enteroblast cells and that loss and gain of Diap1 led to changes in enteroblast numbers. We also found that antagonistic interplay between Notch and EGFR signalling governs enteroblast life/death decisions via the Klumpfuss/WT1 and Lozenge/RUNX transcription regulators, which also regulate enteroblast differentiation and cell fate plasticity. These data provide new insights into how caspases drive adult tissue renewal and protect against the formation of tumours.

The POU/Oct Transcription Factor Nubbin Controls the Balance of Intestinal Stem Cell Maintenance and Differentiation by Isoform-Specific Regulation.

SummaryDrosophila POU/Oct transcription factors are required for many developmental processes, but their putative regulation of adult stem cell activity has not been investigated. Here, we show that Nubbin (Nub)/Pdm1, homologous to mammalian OCT1/POU2F1 and related to OCT4/POU5F1, is expressed in gut epithelium progenitor cells. We demonstrate that the nub-encoded protein isoforms, Nub-PB and Nub-PD, play opposite roles in the regulation of intestinal stem cell (ISC) maintenance and differentiation. Depletion of Nub-PB in progenitor cells increased ISC proliferation by derepression of escargot expression. Conversely, loss of Nub-PD reduced ISC proliferation, suggesting that this isoform is necessary for ISC maintenance, analogous to mammalian OCT4/POU5F1 functions. Furthermore, Nub-PB is required in enteroblasts to promote differentiation, and it acts as a tumor suppressor of Notch RNAi-driven hyperplasia. We suggest that a dynamic and well-tuned expression of Nub isoforms in progenitor cells is required for maintaining gut epithelium homeostasis.

Staufen1 inhibits MyoD translation to actively maintain muscle stem cell quiescence

Tissue regeneration depends on the timely activation of adult stem cells. In skeletal muscle, the adult stem cells maintain a quiescent state and proliferate upon injury. We show that muscle stem cells (MuSCs) use direct translational repression to maintain the quiescent state. High-resolution single-molecule and single-cell analyses demonstrate that quiescent MuSCs express high levels of Myogenic Differentiation 1 (MyoD) transcript in vivo, whereas MyoD protein is absent. RNA pulldowns and costainings show that MyoD mRNA interacts with Staufen1, a potent regulator of mRNA localization, translation, and stability. Staufen1 prevents MyoD translation through its interaction with the MyoD 3'-UTR. MuSCs from Staufen1 heterozygous (Staufen1+/-) mice have increased MyoD protein expression, exit quiescence, and begin proliferating. Conversely, blocking MyoD translation maintains the quiescent phenotype. Collectively, our data show that MuSCs express MyoD mRNA and actively repress its translation to remain quiescent yet primed for activation.

N-cadherin identifies human endometrial epithelial progenitor cells by in vitro stem cell assays

Is there a specific surface marker that identifies human endometrial epithelial progenitor cells with adult stem cell activity using in vitro assays? N-cadherin isolates clonogenic, self-renewing human endometrial epithelial progenitor cells with high proliferative potential that differentiate into cytokeratin+ gland-like structures in vitro and identifies their location in some cells of gland profiles predominantly in basalis endometrium adjacent to the myometrium. Human endometrium contains a small population of clonogenic, self-renewing epithelial cells with high proliferative potential that differentiate into large gland-like structures, but their identity and location is unknown. Stage-specific embryonic antigen-1 (SSEA-1) distinguishes the epithelium of basalis from functionalis and is a marker of human post-menopausal (Post-M) endometrial epithelium. Prospective observational study of endometrial epithelial cells obtained from hysterectomy samples taken from 50 pre-menopausal (Pre-M) and 24 Post-M women, of which 4 were from women who had taken daily estradiol valerate 2 mg/day for 8 weeks prior. Gene profiling was used to identify differentially expressed surface markers between fresh EpCAM (Epithelial Cell Adhesion Molecule)-magnetic bead-selected basalis-like epithelial cells from Post-M endometrium compared with predominantly functionalis epithelial cells from Pre-M endometrium and validated by qRT-PCR. In vitro clonogenicity and self-renewal assays were used to assess the stem/progenitor cell properties of magnetic bead-sorted N-cadherin+ and N-cadherin- epithelial cells. The cellular identity, location and phenotype of N-cadherin+ cells was assessed by dual colour immunofluorescence and confocal microscopy for cytokeratin, proliferative status (Ki-67), ERα, SSEA-1, SOX9 and epithelial mesenchymal transition (EMT) markers on full thickness human endometrium. CDH2 (N-cadherin gene) was one of 11 surface molecules highly expressed in Post-M compared to Pre-M endometrial epithelial cells. N-cadherin+ cells comprise a median 16.7% (n = 8) and 20.2% (n = 5) of Pre-M endometrial epithelial cells by flow cytometry and magnetic bead sorting, respectively. N-cadherin+ epithelial cells from Pre-M endometrium were more clonogenic than N-cadherin- cells (n = 12, P = 0.003), underwent more population doublings (n = 7), showed greater capacity for serial cloning (n = 7) and differentiated into cytokeratin+ gland-like organoids. N-cadherin immunolocalised to the lateral and apical membrane of epithelial cells in the bases of glands in the basalis of Pre-M endometrium and Post-M gland profiles, co-expressing cytokeratin, ERα but not SSEA-1 or SOX9, which localized on gland profiles proximal to N-cadherin+ cells. N-cadherin+ cells were quiescent (Ki-67-) in the basalis and in Post-M endometrial glands and co-localized with EMT markers vimentin and E-cadherin. The raw and processed data files from the gene microarray have been deposited in the National Center for Biotechnology Information Gene Expression Omnibus data set with accession number GSE35221. This is a descriptive study in human endometrium only using in vitro stem cell assays. The differential ability of N-cadherin+ and N-cadherin-cells to generate endometrial glands in vivo was not determined. A small number of uterine tissues analysed contained adenomyosis for which N-cadherin has been implicated in epithelial-EMT. A new marker enriching for human endometrial epithelial progenitor cells identifies a different and potentially more primitive cell population than SSEA-1, suggesting a potential hierarchy of epithelial differentiation in the basalis. Using N-cadherin as a marker, the molecular and cellular characteristics of epithelial progenitor cells and their role in endometrial proliferative disorders including endometriosis, adenomyosis and thin dysfunctional endometrium can be investigated. This research was supported by Cancer Council Victoria grant 491079 (C.E.G.) and Australian National Health and Medical Research Council grants 1021127 (C.E.G.), 1085435 (C.E.G., J.A.D.), 145780 and 288713 (C.N.S.), RD Wright Career Development Award 465121 (C.E.G.), Senior Research Fellowship 1042298 (C.E.G.), the Victorian Government's Operational Infrastructure Support and an Australian Postgraduate Award (HPTN), and China Council Scholarship (L.X.). The authors have nothing to declare.

Elimination of cancer stem cells and reactivation of latent HIV-1 via AMPK activation: Common mechanism of action linking inhibition of tumorigenesis and the potential eradication of HIV-1

Although promising treatments are currently in development to slow disease progression and increase patient survival, cancer remains the second leading cause of death in the United States. Cancer treatment modalities commonly include chemoradiation and therapies that target components of aberrantly activated signaling pathways. However, treatment resistance is a common occurrence and recent evidence indicates that the existence of cancer stem cells (CSCs) may underlie the limited efficacy and inability of current treatments to effectuate a cure. CSCs, which are largely resistant to chemoradiation therapy, are a subpopulation of cancer cells that exhibit characteristics similar to embryonic stem cells (ESCs), including self-renewal, multi-lineage differentiation, and the ability to initiate tumorigenesis. Interestingly, intracellular mechanisms that sustain quiescence and promote self-renewal in adult stem cells (ASCs) and CSCs likely also function to maintain latency of HIV-1 in CD4+ memory T cells. Although antiretroviral therapy is highly effective in controlling HIV-1 replication, the persistence of latent but replication-competent proviruses necessitates the development of compounds that are capable of selectively reactivating the latent virus, a method known as the “shock and kill” approach. Homeostatic proliferation in central CD4+ memory T (TCM) cells, a memory T cell subset that exhibits limited self-renewal and differentiation and is a primary reservoir for latent HIV-1, has been shown to reinforce and stabilize the latent reservoir in the absence of T cell activation and differentiation. HIV-1 has also been found to establish durable and long-lasting latency in a recently discovered subset of CD4+ T cells known as T memory stem (TSCM) cells. TSCM cells, compared to TCM cells, exhibit stem cell properties that more closely match those of ESCs and ASCs, including self-renewal and differentiation into all memory T cell subsets. It is our hypothesis that activation of AMPK, a master regulator of cellular metabolism that plays a critical role in T cell activation and differentiation of ESCs and ASCs, will lead to both T cell activation-induced latent HIV-1 reactivation, facilitating virus destruction, as well as “activation”, differentiation, and/or apoptosis of CSCs, thus inhibiting tumorigenesis. We also propose the novel observation that compounds that have been shown to both facilitate latent HIV-1 reactivation and promote CSC differentiation/apoptosis (e.g. bryostatin-1, JQ1, metformin, butyrate, etc.) likely do so through a common mechanism of AMPK activation.

Dietary Regulation of Adult Stem Cells.

Dietary intake is a critical regulator of organismal physiology and health. Tissue homeostasis and regeneration are dependent on adult tissue stem cells that self-renew and differentiate into the specialized cell types. As stem cells respond to cues from their environment, dietary signals and nutrients influence tissue biology by altering the function and activity of adult stem cells. In this review, we highlight recent studies that illustrate how diverse diets such as caloric restriction, fasting, high fat diets, and ketogenic diets impact stem cell function and their microenvironments. Caloric restriction generally exerts positive effects on adult stem cells, notably increasing stem cell functionality in the intestine and skeletal muscle as well as increasing hematopoietic stem cell quiescence. Similarly, fasting confers protection of intestinal, hematopoietic, and neuronal stem cells against injury. High fat diets induce intestinal stem cell niche independence and stem-like properties in intestinal progenitors, while high fat diets impair hematopoiesis and neurogenesis. Caloric restriction and fasting are generally beneficial to adult stem cell function, while high fat diets impair stem cell function or create opportunities for tumorigenesis. However, the effects of each diet on stem cell biology are complex and vary greatly between tissues. Given the recent interest in developing dietary interventions or mimetics as therapeutics, further studies, including on ketogenic diets, will be essential to understand how adult stem cells respond to diet-induced signals and physiology.

Profiling of Sox4-dependent transcriptome in skin links tumour suppression and adult stem cell activation

Adult stem cells (ASCs) reside in specific niches in a quiescent state in adult mammals. Upon specific cues they become activated and respond by self-renewing and differentiating into newly generated specialised cells that ensure appropriate tissue fitness. ASC quiescence also serves as a tumour suppression mechanism by hampering cellular transformation and expansion (White AC et al., 2014). Some genes restricted to early embryonic development and adult stem cell niches are often potent modulators of stem cell quiescence, and derailed expression of these is commonly associated to cancer (Vervoort SJ et al., 2013). Among them, it has been shown that recommissioned Sox4 expression facilitates proliferation, survival and migration of malignant cells. By generating a conditional Knockout mouse model in stratified epithelia (Sox4cKO mice), we demonstrated a delayed plucking-induced Anagen in the absence of Sox4. Skin global transcriptome analysis revealed a prominent defect in the induction of transcriptional networks that control hair follicle stem cell (HFSC) activation such as those regulated by Wnt/Ctnnb1, Shh, Myc or Sox9, cell cycle and DNA damage response-associated pathways. Besides, Sox4cKO mice are resistant to skin carcinogenesis, thus linking Sox4 to both normal and pathological HFSC activation (Foronda M et al., 2014). Here we provide additional details on the analysis of Sox4-regulated transcriptome in Telogen and Anagen skin. The raw and processed microarray data is deposited in GEO under GSE58155.

A Transcriptional Mechanism Integrating Inputs from Extracellular Signals to Activate Hippocampal Stem Cells

SummaryThe activity of adult stem cells is regulated by signals emanating from the surrounding tissue. Many niche signals have been identified, but it is unclear how they influence the choice of stem cells to remain quiescent or divide. Here we show that when stem cells of the adult hippocampus receive activating signals, they first induce the expression of the transcription factor Ascl1 and only subsequently exit quiescence. Moreover, lowering Ascl1 expression reduces the proliferation rate of hippocampal stem cells, and inactivating Ascl1 blocks quiescence exit completely, rendering them unresponsive to activating stimuli. Ascl1 promotes the proliferation of hippocampal stem cells by directly regulating the expression of cell-cycle regulatory genes. Ascl1 is similarly required for stem cell activation in the adult subventricular zone. Our results support a model whereby Ascl1 integrates inputs from both stimulatory and inhibitory signals and converts them into a transcriptional program activating adult neural stem cells.

Pygo2 regulates β-catenin-induced activation of hair follicle stem/progenitor cells and skin hyperplasia.

Understanding the epigenetic mechanisms that control the activation of adult stem cells holds the promise of tissue and organ regeneration. Hair follicle stem cells have emerged as a prime model to study stem cell activation. Wnt/β-catenin signaling controls multiple aspects of skin epithelial regeneration, with its excessive activity promoting the hyperactivation of hair follicle stem/progenitor cells and tumorigenesis. The contribution of chromatin factors in regulating Wnt/β-catenin pathway function in these processes is unknown. Here, we show that chromatin effector Pygopus homolog 2 (Pygo2) produced by the epithelial cells facilitates depilation-induced hair regeneration, as well as β-catenin-induced activation of hair follicle stem/early progenitor cells and trichofolliculoma-like skin hyperplasia. Pygo2 maximizes the expression of Wnt/β-catenin targets, but is dispensable for β-catenin-mediated expansion of LIM/homeobox protein Lhx2(+) cells, in the stem/early progenitor cell compartment of the hair follicle. Moreover, β-catenin and Pygo2 converge to induce the accumulation and acetylation of tumor suppressor protein p53 upon the cell cycle entry of hair follicle early progenitor cells and in cultured keratinocytes. These findings identify Pygo2 as an important regulator of Wnt/β-catenin function in skin epithelia and p53 activation as a prominent downstream event of β-catenin/Pygo2 action in stem cell activation.

Day–night cycles and the sleep-promoting factor, Sleepless, affect stem cell activity in the Drosophila testis

Adult stem cells maintain tissue integrity and function by renewing cellular content of the organism through regulated mitotic divisions. Previous studies showed that stem cell activity is affected by local, systemic, and environmental cues. Here, we explore a role of environmental day-night cycles in modulating cell cycle progression in populations of adult stem cells. Using a classic stem cell system, the Drosophila spermatogonial stem cell niche, we reveal daily rhythms in division frequencies of germ-line and somatic stem cells that act cooperatively to produce male gametes. We also examine whether behavioral sleep-wake cycles, which are driven by the environmental day-night cycles, regulate stem cell function. We find that flies lacking the sleep-promoting factor Sleepless, which maintains normal sleep in Drosophila, have increased germ-line stem cell (GSC) division rates, and this effect is mediated, in part, through a GABAergic signaling pathway. We suggest that alterations in sleep can influence the daily dynamics of GSC divisions.

Epigenetic regulation in adult stem cells and cancers

Adult stem cells maintain tissue homeostasis by their ability to both self-renew and differentiate to distinct cell types. Multiple signaling pathways have been shown to play essential roles as extrinsic cues in maintaining adult stem cell identity and activity. Recent studies also show dynamic regulation by epigenetic mechanisms as intrinsic factors in multiple adult stem cell lineages. Emerging evidence demonstrates intimate crosstalk between these two mechanisms. Misregulation of adult stem cell activity could lead to tumorigenesis, and it has been proposed that cancer stem cells may be responsible for tumor growth and metastasis. However, it is unclear whether cancer stem cells share commonalities with normal adult stem cells. In this review, we will focus on recent discoveries of epigenetic regulation in multiple adult stem cell lineages. We will also discuss how epigenetic mechanisms regulate cancer stem cell activity and probe the common and different features between cancer stem cells and normal adult stem cells.

Cthrc1 is Involved in the Activation of Adult Stem Cells in Skeletal Muscle

Collagen triple helix repeat containing‐1 (Cthrc1) is a novel protein highly expressed after vascular injury, however the global functionality of the protein remains largely unknown. To determine the role of Cthrc1 in skeletal muscle we have characterized the skeletal muscle phenotype in Cthrc1 overexpressing transgenic (Tg15), knock out (KO) and wildtype (WT) mice. Preliminary characterization of the tibials anterior from KO and WT 12‐week old males identified a reduction in Type I muscle fiber size (KO vs. WT) with no change in distribution of Type I and Type II muscle fibers (as shown by cytochrome oxidase staining). Immunohistochemistry of the gastrocnemius from Tg15 and WT animals showed colocalization of activated Pax7+ satellite cells with both Cthrc1 and myogenin expression, suggesting that Cthrc1 correlates with stem cell activation. Tg15 muscles showed signs of active fiber regeneration, both basophilic cytoplasm and nuclear chains, possibly as a result of increased Cthrc1 expression leading to an increased number of activated stem cells within the tissue. Muscle stem cell populations dual‐labeled for Sca‐1 and CD31 were evaluated by flow cytometry; KO animals showed a significant reduction in the Sca‐1+/CD31− cell population when compared to wildtype animals. C2C12 myoblasts cultured in Cthrc1 conditioned media show increased transcript levels of muscle regulatory factors (MRF) Myf5 and myogenin when compared to controls; consistent with our animal data. The difference between Sca‐1+ MSCs, coupled with the influence of Cthrc1 on MRF expression suggests that Cthrc1 may affect MSC activation as well as proliferation. Cthrc1's potential to act as an MSC activator suggests it may play a significant role in skeletal muscle repair and regeneration offering new therapeutic approaches to fibrotic and muscle wasting diseases.

MRNA-expression of ERα, ERβ, and PR in clonal stem cell cultures obtained from human endometrial biopsies.

Background. Proliferation and differentiation of the endometrium are regulated by estrogen and progesterone. The enormous regenerative capacity of the endometrium is thought to be based on the activity of adult stem cells. However, information on endocrine regulatory mechanisms in human endometrial stem cells is scarce. In the present study, we investigated the expression of ERα, ERβ, and PR in clonal cultures of human endometrial stem cells derived from transcervical biopsies. Methods. Endometrial tissue of 11 patients was obtained by transcervical biopsy. Stromal cell suspensions were plated at clonal density and incubated for 15 days. Expression of ERα, ERβ and PR was determined by qPCR prior to and after one cloning round, and normalized to 18 S rRNA expression. Results. Expression of ERα and ERβ was downregulated by 64% and 89%, respectively (P = 0.002 and P < 0.001). In contrast, PR was not significantly downregulated, due to a more heterogenous expression pattern. Conclusions. Culture of human endometrial stroma cells results in a downregulation of ERα and ERβ, while expression of PR remained unchanged in our patient collective. These results support the hypothesis that stem cells may not be subject to direct stimulation by sex steroids, but rather by paracrine mechanisms within the stem cell niche.

Adult stem cells in the endometrium

Rare cells with adult stem cell activity were recently discovered in human endometrium. Endometrial stem/progenitor cell candidates include epithelial, mesenchymal and endothelial cells, and all may contribute to the rapid endometrial regeneration following menstruation, rather than a single candidate. Endometrial mesenchymal stem-like cells (eMSC) are prospectively isolated as CD146(+)PDGF-Rβ(+) cells and are found in both basalis and functionalis as perivascular cells. Epithelial progenitor cells are detected in colony forming unit assays but their identity awaits elucidation. They are postulated to reside in the basalis in gland bases. Endometrial stem/progenitor cells may be derived from endogenous stem cells, but emerging evidence suggests a bone marrow contribution. Endometrial endothelial progenitor cells are detected as side population cells, which express several endothelial cell markers and differentiate into endometrial glandular epithelial, stromal and endothelial cells. Investigating endometrial stem cell biology is crucial to understanding normal endometrial physiology and to determine their roles in endometrial proliferative diseases. The nature of endometriosis suggests that initiation of ectopic endometrial lesions involves endometrial stem/progenitor cells, a notion compatible with Sampson's retrograde menstruation theory and supported by the demonstration of eMSC in menstrual blood. Evidence of cancer stem cells (CSC) in endometrial cancer indicates that new avenues for developing therapeutic options targeting CSC may become available. We provide an overview of the accumulating evidence for endometrial stem/progenitor cells and their possible roles in endometrial proliferative disorders, and discuss the unresolved issues.