Stem cells in epithelial tissues

Liver organoids and their application in liver cancer research

Liver cancer, a common and intractable liver-related disease, is a malignant tumor with a high morbidity, which needs a high treatment cost but still lacks perfect clinical treatment methods. Looking for an effective platform for liver cancer study and drug screening is urgent and important. Traditional analytical methods for liver disease studies mainly rely on the 2D cell culture and animal experiments, which both cannot fully recapitulate physiological and pathological processes of human liver. For example, cell culture can only show basic functions of cells in vitro, while animal models always hold the problem of species divergence. The organoids, a 3D invitro culture system emerged in recent years, is a cell-bound body with different cell types and has partial tissue functions. The organoid technology can reveal the growth state, structure, function and characteristics of the tissue or organ, and plays an important role in reconstructing invitro experimental models that can truly simulate the human liver. In this paper, we will give a brief introduction of liver organoids and review their applications in liver cancer research, especially in liver cancer pathogenesis, drug screening, precision medicine, regenerative medicine, and other fields. We have also discussed advantages and disadvantages of organoids, as well as future directions and perspectives towards liver organoids.

Challenges and opportunities in cell expansion for cultivated meat

The cultivation of meat using in vitro grown animal stem cells offers a promising solution to pressing global concerns around climate change, ethical considerations, and public health. However, cultivated meat introduces an unprecedented necessity: the generation of mass scales of cellular biomaterial, achieved by fostering cell proliferation within bioreactors. Existing methods for in vitro cell proliferation encounter substantial challenges in terms of both scalability and economic viability. Within this perspective, we discuss the current landscape of cell proliferation optimization, focusing on approaches pertinent to cellular agriculture. We examine the mechanisms governing proliferation rates, while also addressing intrinsic and conditional rate limitations. Furthermore, we expound upon prospective strategies that could lead to a significant enhancement of the overall scalability and cost-efficiency of the cell proliferation phase within the cultivated meat production process. By exploring knowledge from basic cell cycle studies, pathological contexts and tissue engineering, we may identify innovative solutions toward optimizing cell expansion.

Biomaterials and bioengineering to guide tissue morphogenesis in epithelial organoids

Organoids are self-organized and miniatured in vitro models of organs and recapitulate key aspects of organ architecture and function, leading to rapid progress in understanding tissue development and disease. However, current organoid culture systems lack accurate spatiotemporal control over biochemical and physical cues that occur during in vivo organogenesis and fail to recapitulate the complexity of organ development, causing the generation of immature organoids partially resembling tissues in vivo. Recent advances in biomaterials and microengineering technologies paved the way for better recapitulation of organ morphogenesis and the generation of anatomically-relevant organoids. For this, understanding the native ECM components and organization of a target organ is essential in providing rational design of extracellular scaffolds that support organoid growth and maturation similarly to the in vivo microenvironment. In this review, we focus on epithelial organoids that resemble the spatial distinct structure and function of organs lined with epithelial cells including intestine, skin, lung, liver, and kidney. We first discuss the ECM diversity and organization found in epithelial organs and provide an overview of developing hydrogel systems for epithelial organoid culture emphasizing their key parameters to determine cell fates. Finally, we review the recent advances in tissue engineering and microfabrication technologies including bioprinting and microfluidics to overcome the limitations of traditional organoid cultures. The integration of engineering methodologies with the organoid systems provides a novel approach for instructing organoid morphogenesis via precise spatiotemporal modulation of bioactive cues and the establishment of high-throughput screening platforms.

Single-cell analysis defines the lineage plasticity of stem cells in cervix epithelium

Information about the dynamic change and post-injury regeneration of cervical epithelium is relatively rare, even though it is tightly related to gynecologic malignancy. Here, using a feeder cell-based culturing system, we stably cloned mouse and human P63 and KRT5 expressing cells from the adult cervix as putative cervical stem/progenitor cells (CVSCs). When subjected to differentiation, the cultured cells gave rise to mature cervical epithelium by differentiating into squamous or glandular cells. The ability of endogenous mouse CVSCs to reconstitute cervical epithelium after injury was also evident from the genetic lineage tracing experiments. Single-cell transcriptomic analysis further classified the CVSCs into three subtypes and delineated their bi-lineage differentiation roadmap by pseudo-time analysis. We also tracked the real-time differentiation routes of two representing single CVSC lines in vitro and found that they recapitulated the predicted roadmap in pseudo-time analysis. Signaling pathways including Wnt, TGF-beta, Notch and EGFR were found to regulate the cervical epithelial hierarchy and implicated the different roles of distinct types of cells in tissue homeostasis and tumorigenesis. Collectively, the above data provide a cloning system to achieve stable in vitro culture of a bi-lineage stem/progenitor cell population in the cervix, which has profound implications for our understanding of the cervix stem/progenitor cell function in homeostasis, regeneration, and disease and could be helpful for developing stem cell-based therapies in future.

CTIP2 and lipid metabolism: regulation in skin development and associated diseases

INTRODUCTION

COUP-TF INTERACTING PROTEIN 2 (CTIP2) is a crucial transcription factor exhibiting its control through coupled modulation of epigenetic modification and transcriptional regulation of key genes related to skin, immune, and nervous system development. Previous studies have validated the essential role of CTIP2 in skin development and maintenance, propagating its effects in epidermal permeability barrier (EPB) homeostasis, wound healing, inflammatory diseases, and epithelial cancers. Lipid metabolism dysregulation, on the other hand, has also established its independent emerging role over the years in normal skin development and various skin-associated ailments. This review focuses on the relatively unexplored connections between CTIP2-mediated control of lipid metabolism and alteration of EPB homeostasis, delayed wound healing, inflammatory diseases exacerbation, and cancer promotion and progression.

AREAS COVERED

Here we have discussed the intricate interplay of various endogenous lipids and lipoproteins accompanying skin development and associated disease processes and the possible link to CTIP2-mediated regulation of lipid metabolism.

EXPERT OPINION

Establishing the link between CTIP2 and lipid metabolism alterations in the context of skin morphogenesis and diverse types of skin diseases including cancer can help us identify novel targets for effective therapeutic intervention.

An Intermediate Concentration of Calcium with Antioxidant Supplement in Culture Medium Enhances Proliferation and Decreases the Aging of Bone Marrow Mesenchymal Stem Cells

Human bone marrow stem cells (HBMSCs) are isolated from the bone marrow. Stem cells can self-renew and differentiate into various types of cells. They are able to regenerate kinds of tissue that are potentially used for tissue engineering. To maintain and expand these cells under culture conditions is difficult—they are easily triggered for differentiation or death. In this study, we describe a new culture formula to culture isolated HBMSCs. This new formula was modified from NCDB 153, a medium with low calcium, supplied with 5% FBS, extra growth factor added to it, and supplemented with N-acetyl-L-cysteine and L-ascorbic acid-2-phosphate to maintain the cells in a steady stage. The cells retain these characteristics as primarily isolated HBMSCs. Moreover, our new formula keeps HBMSCs with high proliferation rate and multiple linage differentiation ability, such as osteoblastogenesis, chondrogenesis, and adipogenesis. It also retains HBMSCs with stable chromosome, DNA, telomere length, and telomerase activity, even after long-term culture. Senescence can be minimized under this new formulation and carcinogenesis of stem cells can also be prevented. These modifications greatly enhance the survival rate, growth rate, and basal characteristics of isolated HBMSCs, which will be very helpful in stem cell research.

The Reconstructed Human Epidermis in vitro — a Model for Basic and Applied Research of Human Skin

Background. The reconstructed human epidermis (RE) is an in vitro tissue-engineering construct similar to the native epidermis. Objective. To develop a full-layer RE. Describe its structure: determine the presence of all layers of the epidermal component, including basal, spinous and granular layers and stratum corneum of the epidermis; detect the basement membrane, the border between the epidermal and mesenchymal component. Materials and methods. Isolation of keratinocytes and fibroblasts from human donor skin. Cultivation of keratinocytes and fibroblasts in vitro under 2D conditions, cell subculturing and 3D modeling of RE, obtaining cryosections, histological staining, immunohistochemical (IHC) study with antibodies to cytokeratins 14 and 10, Ki67 protein, loricrin, laminin 5 and plectin. Results. A technique was developed for the formation of RE. Histological examination showed that the stratification of keratinocyte layers occurs during the formation of RE. Layers are formed including basal, spinous and granular layers and stratum corneum. The IHC study has shown the proliferative activity of keratinocytes of the basal layer and has detected the presence of marker proteins of keratinocytes at different stages of differentiation. RE basal keratinocytes, like native ones, form hemidesmosomes and synthesize basement membrane proteins. Conclusions. A full-layer human RE was obtained in vitro. RE meets all the characteristics of the native epidermis and it is suitable for basic and practical research in the field of skin biology, dermatology, and cosmetology.

Cell-based therapies for the treatment of myocardial infarction: lessons from cardiac regeneration and repair mechanisms in non-human vertebrates

Ischemic cardiomyopathy is the cardiovascular condition with the highest impact on the Western population. In mammals (humans included), prolonged ischemia in the ventricular walls causes the death of cardiomyocytes (myocardial infarction, MI). The loss of myocardial mass is soon compensated by the formation of a reparative, non-contractile fibrotic scar that ultimately affects heart performance. Despite the enormous clinical relevance of MI, no effective therapy is available for the long-term treatment of this condition. Moreover, since the human heart is not able to undergo spontaneous regeneration, many researchers aim at designing cell-based therapies that allow for the substitution of dead cardiomyocytes by new, functional ones. So far, the majority of such strategies rely on the injection of different progenitor/stem cells to the infarcted heart. These cardiovascular progenitors, which are expected to differentiate into cardiomyocytes de novo, seldom give rise to new cardiac muscle. In this context, the most important challenge in the field is to fully disclose the molecular and cellular mechanisms that could promote active myocardial regeneration after cardiac damage. Accordingly, we suggest that such strategy should be inspired by the unique regenerative and reparative responses displayed by non-human animal models, from the restricted postnatal myocardial regeneration abilities of the murine heart to the full ventricular regeneration of some bony fishes (e.g., zebrafish). In this review article, we will discuss about current scientific approaches to study cardiac reparative and regenerative phenomena using animal models.

Characterization of Gastrospheres Using 3D Coculture System

To understand the molecular mechanisms involved in gastric disorders and regeneration, we need an in vitro tridimensional (3D) culture model, which can mimic the in vivo gastric microenvironment. A 3D coculture system named gastrosphere is proposed herein, composed of primary human gastric epithelial and stromal cells. The primary cultures were obtained from endoscopic gastric biopsies, and after mechanical and enzymatic dispersion, epithelial (HGE3) and stromal (HGS12) cells were expanded. After extensive immunocytochemical characterization, cells were seeded onto 96-well round bottom plates previously covered with 1% agarose. Cells were cultured in KM-F12 culture medium with 10% fetal bovine serum (FBS), antibiotics, and antimycotics, in humidified air at 37 °C and atmosphere containing 5% CO₂ for 72 h or until spheres formation. Then gastrospheres were carefully transferred to a rotary cell culture system (RCCS-4), and maintained for 07, 14, 21, and 28 days. Gastrospheres were morphologically characterized by immunocytochemistry [cytokeratins (CK), vimentin, α-smooth muscle actin (α-SMA), laminin (LN), fibronectin (FN), and type IV collagen (CIV), proliferating cell nuclear antigen (PCNA)], and electron microscopy. In gastrospheres, the cytokeratin-positive epithelial cells were found in the outer layer, while vimentin-positive stromal cells were localized in the center of the gastrospheres. PCNA+ cells were mainly seen at the peripheral and in the intermediary region while nestin+ cells were also depicted in the latter zone. Scanning electron microscopy revealed groups of cohesive gastric cells at the periphery, while transmission electron microscopy demonstrated some differentiated mucous-like or zymogenic-like cells in the periphery and stromal structures located at the center of the 3D structures. Extracellular matrix was deposed between cells. Our data suggest that in vitro gastrospheres recapitulate the in vivo gastric microenvironment.

The march of pluripotent stem cells in cardiovascular regenerative medicine

Cardiovascular disease (CVD) continues to be the leading cause of global morbidity and mortality. Heart failure remains a major contributor to this mortality. Despite major therapeutic advances over the past decades, a better understanding of molecular and cellular mechanisms of CVD as well as improved therapeutic strategies for the management or treatment of heart failure are increasingly needed. Loss of myocardium is a major driver of heart failure. An attractive approach that appears to provide promising results in reducing cardiac degeneration is stem cell therapy (SCT). In this review, we describe different types of stem cells, including embryonic and adult stem cells, and we provide a detailed discussion of the properties of induced pluripotent stem cells (iPSCs). We also present and critically discuss the key methods used for converting somatic cells to pluripotent cells and iPSCs to cardiomyocytes (CMs), along with their advantages and limitations. Integrating and non-integrating reprogramming methods as well as characterization of iPSCs and iPSC-derived CMs are discussed. Furthermore, we critically present various methods of differentiating iPSCs to CMs. The value of iPSC-CMs in regenerative medicine as well as myocardial disease modeling and cardiac regeneration are emphasized.

Human trophoblast stem cell self-renewal and differentiation: Role of decorin

The origin and regulation of stem cells sustaining trophoblast renewal in the human placenta remain unclear. Decorin, a leucine-rich proteoglycan restrains trophoblast proliferation, migration/invasiveness and endovascular differentiation, and local decorin overproduction is associated with preeclampsia (PE). Here, we tested the role of decorin in human trophoblast stem cell self-renewal and differentiation, using two models: an immortalized first trimester trophoblast cell line HTR-8/SVneo (HTR) and freshly isolated primary trophoblast (p-trophoblast) from early first trimester (6-9 weeks) placentas. Self-renewal capacity was measured by spheroid forming ability of single cells on ultra-low attachment plates for multiple generations. Markers of embryonic stem (ES) cells, trophoblast stem (TS) cells and trophoblast were used to identify stem cell hierarchy. Differentiation markers for syncytial and extravillous (EVT) pathways were employed to identify differentiated cells. Bewo cells were additionally used to explore DCN effects on syncytialization. Results reveal that the incidence of spheroid forming stem-like cells was 13-15% in HTR and 0.1-0.4%, in early first trimester p-trophoblast, including a stem cell hierarchy of two populations of ES and TS-like cells. DCN restrained ES cell self-renewal, promoted ES to TS transition and maintenance of TS cell stem-ness, but inhibited TS cell differentiation into both syncytial and EVT pathways.

SOXF factors regulate murine satellite cell self-renewal and function through inhibition of β-catenin activity

Muscle satellite cells are the primary source of stem cells for postnatal skeletal muscle growth and regeneration. Understanding genetic control of satellite cell formation, maintenance, and acquisition of their stem cell properties is on-going, and we have identified SOXF (SOX7, SOX17, SOX18) transcriptional factors as being induced during satellite cell specification. We demonstrate that SOXF factors regulate satellite cell quiescence, self-renewal and differentiation. Moreover, ablation of Sox17 in the muscle lineage impairs postnatal muscle growth and regeneration. We further determine that activities of SOX7, SOX17 and SOX18 overlap during muscle regeneration, with SOXF transcriptional activity requisite. Finally, we show that SOXF factors also control satellite cell expansion and renewal by directly inhibiting the output of β-catenin activity, including inhibition of Ccnd1 and Axin2. Together, our findings identify a key regulatory function of SoxF genes in muscle stem cells via direct transcriptional control and interaction with canonical Wnt/β-catenin signaling.

Blurring nature at its boundaries. Vague phenomena in current stem cell debate

This paper illuminates the explanatory role of vagueness und species membership against the background of scientific developments in recent stem cell research. With the help of the Neo-Aristotelian concept of "life form naturalism" ontologically vague entities such as stem cells, all above induced pluripotent stem cells (iPS), could be described as necessary constituents for the correct sorting and naming of natural processes and its bearers. Furthermore this specific assessment allows drawing some important ontological and ethical consequences.

Dual roles of yes-associated protein (YAP) in colorectal cancer

Yes-associated protein (YAP) is a downstream effector molecule of a newly emerging tumour suppressor pathway called the Hippo pathway. YAP is a transcriptional co-activator and mis-expressed in various cancers, including colorectal cancer (CRC). Accumulating studies show that the high expression of nuclear YAP is linked with tumour progression and decreased survival. Nuclear YAP can interact with other transcription factors to promote cancer cell proliferation, apoptosis, metastasis and maintenance of stemness. Therefore, YAP has the potential to be a tumour biomarker or therapeutic target for CRC. However, recently, a number of studies have supported a contradictory role for YAP as a tumour suppressor, demonstrating inhibition of the tumorigenesis of CRC, involvement in promoting cell apoptosis, and inhibiting the maintenance of intestinal stem cells and inflammatory activity. In these studies, high expression of YAP was highly correlated with worse survival in CRC. In this review, we will comprehensively summarize and analyse these paradoxical reports, and discuss both the oncogenic and tumour suppressor functions of YAP in the differential status of CRC progression. Further investigation into the mechanisms responsible for the dual function of YAP will be of great value in the prevention, early diagnosis, and therapy of CRC.

Stem and progenitor cells: advancing bone tissue engineering

Unlike many other postnatal tissues, bone can regenerate and repair itself; nevertheless, this capacity can be overcome. Traditionally, surgical reconstructive strategies have implemented autologous, allogeneic, and prosthetic materials. Autologous bone--the best option--is limited in supply and also mandates an additional surgical procedure. In regenerative tissue engineering, there are myriad issues to consider in the creation of a functional, implantable replacement tissue. Importantly, there must exist an easily accessible, abundant cell source with the capacity to express the phenotype of the desired tissue, and a biocompatible scaffold to deliver the cells to the damaged region. A literature review was performed using PubMed; peer-reviewed publications were screened for relevance in order to identify key advances in stem and progenitor cell contribution to the field of bone tissue engineering. In this review, we briefly introduce various adult stem cells implemented in bone tissue engineering such as mesenchymal stem cells (including bone marrow- and adipose-derived stem cells), endothelial progenitor cells, and induced pluripotent stem cells. We then discuss numerous advances associated with their application and subsequently focus on technological advances in the field, before addressing key regenerative strategies currently used in clinical practice. Stem and progenitor cell implementation in bone tissue engineering strategies have the ability to make a major impact on regenerative medicine and reduce patient morbidity. As the field of regenerative medicine endeavors to harness the body's own cells for treatment, scientific innovation has led to great advances in stem cell-based therapies in the past decade.

Contribution of immunomodulators to gastroesophageal reflux disease and its complications: stromal cells, interleukin 4, and adiponectin

Gastroesophageal reflux disease (GERD) has become the most commonly seen gastrointestinal disorder in outpatient clinics. In the United States, around 20% of the general population experience heartburn on a weekly basis. Although clinical complaints can be mild or moderate, patients with GERD may develop further complications, such as peptic strictures, Barrett's esophagus (BE), and even esophageal adenocarcinoma. Pathologically, GERD is developed as a result of chronic and enhanced exposure of the esophageal epithelium to noxious gastric refluxate. In this review article, we provide an overview of GERD and then focus on the roles of stromal cells, interleukin 4, and adiponectin in GERD and BE. The importance of inflammation and immunomodulators in GERD pathogenesis is highlighted. Targeting the immunomodulators or inflammation in general may improve the therapeutic outcome of GERD, in particular, in those refractory to proton pump inhibitors.

Aneuploidy in stem cells

Stem cells hold enormous promise for regenerative medicine as well as for engineering of model systems to study diseases and develop new drugs. The discovery of protocols that allow for generating induced pluripotent stem cells (IPSCs) from somatic cells has brought this promise steps closer to reality. However, as somatic cells might have accumulated various chromosomal abnormalities, including aneuploidies throughout their lives, the resulting IPSCs might no longer carry the perfect blueprint for the tissue to be generated, or worse, become at risk of adopting a malignant fate. In this review, we discuss the contribution of aneuploidy to healthy tissues and how aneuploidy can lead to disease. Furthermore, we review the differences between how somatic cells and stem cells respond to aneuploidy.

Epithelial expression of cytokeratins 15 and 19 in vitiligo

BACKGROUND

Cytokeratins (CK) belong to the family of intermediate filament proteins, and among them specific epithelial keratins are considered markers for stem cells activation.

OBJECTIVES

This study aims to investigate the expression of CK15 and CK19 as possible stem cell markers in vitiligo during phototherapy.

METHODS

The study was conducted on vitiligo patients receiving narrow-band ultraviolet therapy. Immunohistochemical staining for CK15 and CK19 was carried out, and clinical follow-up continued for 4 weeks.

RESULTS

Of 28 patients, CK15 expression was demonstrated in 17 cases (61%) while CK19 expression was demonstrated in 11 cases (39%). Cells expressing positive staining were demonstrated in follicular and interfollicular epithelium. Expression was clearly demonstrated in patients younger than 20 years old, with shorter disease duration, with disease stability, and with normally pigmented hairs. Expression of cytokeratins was significantly correlated to improvement of vitiligo lesions.

CONCLUSION

CK15 and CK19 are expressed in vitiligo during UV repigmentation in the follicular and interfollicular epithelium. This expression of cytokeratins was significantly correlated to improvement and can be considered valuable tool to monitor stem cells stimulation for the sake of the repigmentation process in vitiligo.

Immunofluorescence Tomography of Mouse Ocular Surface Epithelial Stem Cells and Their Niche Microenvironment

PURPOSE

Currently, there are no definitive immunomarkers for epithelial stem cells (corneal and conjunctival) or their poorly understood niche microenvironment. The H2B-GFP/K5tTA mouse enables visualization of label-retaining cells (LRCs), which exhibit the functional marker of stem cell quiescence. We used immunofluorescence tomography to evaluate putative stem cell markers and LRCs of the mouse ocular surface.

METHODS

H2B-GFP/K5tTA mice were pulsed for 56 days and then chased with doxycycline to label LRCs. Limbus and eyelid tissue was 3-dimensionally (3-D) reconstructed using immunofluorescence tomography to identify and characterize LRCs using the putative stem cell markers sox9, keratin 19, lrig1, blimp1, and abcb5.

RESULTS

After 28 days of chase, LRCs were localized to the entire limbus epithelium and, infrequently, the anterior limbal stroma. Label-retaining cells comprised 3% of limbal epithelial cells after 56 days of chase. Conjunctival LRCs were localized to the fornix and comprised 4% of the total fornix epithelial cells. No stem cell immunomarker was specific for ocular surface LRCs; however, blimp1 enriched for limbal basal epithelial cells and 100% of green fluorescent protein-positive (GFP+) cells at the limbus and fornix were found to be lrig1-positive.

CONCLUSIONS

Label-retaining cells represent a larger population of the mouse limbus than previously thought. They decrease in number with increased doxycycline chase, suggesting that LRC populations with different cell cycle lengths exist at the limbus. We conclude that current immunomarkers are unable to colocalize with the functional marker of epithelial stem cell quiescence; however, blimp1 may enrich for limbal epithelial basal cells.

Mesenchymal stem cells: Identification, phenotypic characterization, biological properties and potential for regenerative medicine through biomaterial micro-engineering of their niche

Mesenchymal stem cells (MSCs) are multipotent stem cells. Although they were originally identified in bone marrow and described as 'marrow stromal cells', they have since been identified in many other anatomical locations in the body. MSCs can be isolated from bone marrow, adipose tissue, umbilical cord and other tissues but the richest tissue source of MSCs is fat. Since they are adherent to plastic, they may be expanded in vitro. MSCs have a distinct morphology and express a specific set of CD (cluster of differentiation) molecules. The phenotypic pattern for the identification of MSCs cells requires expression of CD73, CD90, and CD105 and lack of CD34, CD45, and HLA-DR antigens. Under appropriate micro-environmental conditions MSCs can proliferate and give rise to other cell types. Therefore, they are ideally suited for the treatment of systemic inflammatory and autoimmune conditions. They have also been implicated as key players in regenerating injured tissue following injury and trauma. MSC populations isolated from adipose tissue may also contain regulatory T (Treg) cells, which have the capacity for modulating the immune system. The immunoregulatory and regenerative properties of MSCs make them ideal for use as therapeutic agents in vivo. In this paper we review the literature on the identification, phenotypic characterization and biological properties of MSCs and discuss their potential for applications in cell therapy and regenerative medicine. We also discuss strategies for biomaterial micro-engineering of the stem cell niche.

Radiation responses of stem cells: targeted and non-targeted effects

Stem cells are fundamental to the development of any tissue or organism via their ability to self-renew, which is aided by their unlimited proliferative capacity and their ability to produce fully differentiated offspring, often from multiple lineages. Stems cells are long lived and have the potential to accumulate mutations, including in response to radiation exposure. It is thought that stem cells have the potential to be induced into a cancer stem cell phenotype and that these may play an important role in resistance to radiotherapy. For radiation-induced carcinogenesis, the role of targeted and non-targeted effects is unclear with tissue or origin being important. Studies of genomic instability and bystander responses have shown consistent effects in haematopoietic models. Several models of radiation have predicted that stem cells play an important role in tumour initiation and that bystander responses could play a role in proliferation and self-renewal.

Identification and characterization of an injury-induced skeletal progenitor

The postnatal skeleton undergoes growth, remodeling, and repair. We hypothesized that skeletal progenitor cells active during these disparate phases are genetically and phenotypically distinct. We identified a highly potent regenerative cell type that we term the fracture-induced bone, cartilage, stromal progenitor (f-BCSP) in the fracture callus of adult mice. The f-BCSP possesses significantly enhanced skeletogenic potential compared with BCSPs harvested from uninjured bone. It also recapitulates many gene expression patterns involved in perinatal skeletogenesis. Our results indicate that the skeletal progenitor population is functionally stratified, containing distinct subsets responsible for growth, regeneration, and repair. Furthermore, our findings suggest that injury-induced changes to the skeletal stem and progenitor microenvironments could activate these cells and enhance their regenerative potential.

Superior Potential of CD34-Positive Cells Compared to Total Mononuclear Cells for Healing of Nonunion following Bone Fracture

We recently demonstrated that the local transplantation of human peripheral blood (PB) CD34+ cells, an endothelial/hematopoietic progenitor cell-rich population, contributes to fracture repair via vasculogenesis/angiogenesis and osteogenesis. Human PB mononuclear cells (MNCs) are also considered a potential cell fraction for neovascularization. We have previously shown the feasibility of human PB MNCs to enhance fracture healing. However, there is no report directly comparing the efficacy for fracture repair between CD34+ cells and MNCs. In addition, an unhealing fracture model, which does not accurately resemble a clinical setting, was used in our previous studies. To overcome these issues, we compared the capacity of human granulocyte colony-stimulating factor-mobilized PB (GM-PB) CD34+ cells and human GM-PB MNCs in a nonunion model, which more closely resembles a clinical setting. First, the effect of local transplantation of 1 × 105 GM-PB CD34+ cells (CD34+ group), 1 × 107 GM-PB MNCs (containing approximately 1 × 105 GM-PB CD34+ cells) (MNC group), and phosphate-buffered saline (PBS) (PBS group) on nonunion healing was compared. Similar augmentation of blood flow recovery at perinonunion sites was observed in the CD34+ and MNC groups. Meanwhile, a superior effect on nonunion repair was revealed by radiological, histological, and functional assessment in the CD34+ group compared with the other groups. Moreover, through in vivo and in vitro experiments, excessive inflammation induced by GM-PB MNCs was confirmed and believed to be one of the mechanisms underlying this potency difference. These results strongly suggest that local transplantation of GM-PB CD34+ cells is a practical and effective strategy for treatment of nonunion after fracture.

Latent progenitor cells as potential regulators for tympanic membrane regeneration

Tympanic membrane (TM) perforation, in particular chronic otitis media, is one of the most common clinical problems in the world and can present with sensorineural healing loss. Here, we explored an approach for TM regeneration where the latent progenitor or stem cells within TM epithelial layers may play an important regulatory role. We showed that potential TM stem cells present highly positive staining for epithelial stem cell markers in all areas of normal TM tissue. Additionally, they are present at high levels in perforated TMs, especially in proximity to the holes, regardless of acute or chronic status, suggesting that TM stem cells may be a potential factor for TM regeneration. Our study suggests that latent TM stem cells could be potential regulators of regeneration, which provides a new insight into this clinically important process and a potential target for new therapies for chronic otitis media and other eardrum injuries.

Identification of pluripotent cells in bovine uterus: in situ and in vitro studies

The aim of this study was to identify uterine pluripotent cells both in bovine uterine tissues as well in epithelial, stromal, and myometrial uterine cell populations. Moreover, the relationship of pluripotent markers expression with age and the uterine horn side was considered. Uterine tissue was collected from ipsilateral and contralateral horns (days 8–10 of the estrous cycle). Immunohistostaining for C-KIT, OCT3/4, NANOG, and SOX2 in uterine tissue was determined. mRNA expression of C-KIT, OCT3/4, NANOG and SOX2 was evaluated in uterine tissue relative to the age of the cow and uterine horn side. Gene and protein expression of these markers in the uterine luminal epithelial, stromal, and myometrial cells was evaluated by real-time PCR and western blotting respectively. The expression of pluripotent cell markers OCT3/4, NANOG, and SOX2 was identified by flow cytometry assay in epithelial, stromal, and myometrial cells. Multilineage differentiation of the bovine uterine cells was performed. mRNA expression of OCT3/4, NANOG, and SOX2 in uterine tissue was higher in the ipsilateral horn than in the contralateral horn. Flow cytometry assay revealed positive fluorescence for OCT3/4, NANOG, and SOX2 in all uterine cell types. Results showed the age-dependent expression of pluripotent markers in uterine tissue. Beside, the different expression of pluripotent cells in each horn of uterus suggests the influence of ovarian hormones on these characteristics. The highest mRNA and protein expression for pluripotent markers was observed in stromal cells among uterine cells, which indicates this population of cells as the main site of pluripotent cells in the cow uterus.

Human dental pulp stem cells cultured onto dentin derived scaffold can regenerate dentin-like tissue in vivo

Regeneration of dentin tissues in the pulp space of teeth serves the ultimate goal of preserving teeth via endodontic approaches. In recent times, many studies suggested that human dentin scaffolds combined with dental stem cells was a potential strategy for the complete dentin tissue regeneration. In this study, human dental pulp stem cells (DPSCs) were isolated and cultured. Dentin specimens were prepared from human third molars and treated with ethylene diamine tetra-acetic acid and citric acid to remove the smear layer. Then, DPSCs were cultured onto human treated dentin (hTD) and implanted in mouse model for 4, 6 and 8 weeks. The resulting grafts were assessed by hematoxylin and eosin stain and immunohistochemical stains. As a result, DPSCs were supported and induced to regenerate of dentin-like tissues which expressed specific dentin markers such as dentin sialophosphoprotein and dentin matrix protein 1 by combination with hTD in vivo. Furthermore, cells existed in the newly-formed dentin-like tissues also expressed typical human mitochondria antibodies, demonstrated that new tissues originated from human. In conclusion, the obtain results extend hopefully newly-established therapy to apply in endodontics and traumatic dental hard tissues.

Evaluation of embryonic age and the effects of different proteases on the isolation and primary culture of chicken intestinal epithelial cells in vitro

The present study evaluates the effects of embryonic age and proteolytic enzymes on the isolation and primary culture of chicken enterocyte and to establish an effective technique for chicken intestinal epithelial cell (IEC) cultivation. Fourteen-day-old, 16-day-old and 18-day-old embryos (average weight: 52.23 ± 0.76 g, 50.86 ± 0.99 g, 48.98 ± 1.03 g) were the source for preparation of enterocyte culture, and trypsin-ethylene diamine tetraacetic acid, collagenase, thermolysin and combination of collagenase and thermolysin were used for digestion medium. Optimal culture protocols were determined by qualitative assays of proliferation. Cells isolated by using 14-day-old embryo and collagenase obtain the best attachment and growth in culture, and the production of continuously growing IEC cultures. Thus, we conclude that the use of collagenase as a dissociating enzyme and 14-day-old embryo as a source can be advantageously applied to the isolation of chicken IEC and this method may be useful for various applications and basic studies of the intestinal tract concerning such objects as physiology, immunology and toxicology.

Deer antler--a novel model for studying organ regeneration in mammals

Deer antler is the only mammalian organ that can fully grow back once lost from its pedicle - the base from which it grows. Therefore, antlers probably offer the most pertinent model for studying organ regeneration in mammals. This paper reviews our current understanding of the mechanisms underlying regeneration of antlers, and provides insights into the possible use for human regenerative medicine. Based on the definition, antler renewal belongs to a special type of regeneration termed epimorphic. However, histological examination failed to detect dedifferentiation of any cell type on the pedicle stump and the formation of a blastema, which are hallmark features of classic epimorphic regeneration. Instead, antler regeneration is achieved through the recruitment, proliferation and differentiation of the single cell type in the pedicle periosteum (PP). The PP cells are the direct derivatives of cells resident in the antlerogenic periosteum (AP), a tissue that exists in prepubertal deer calves and can induce ectopic antler formation when transplanted elsewhere on the deer body. Both the AP and PP cells express key embryonic stem cell markers and can be induced to differentiate into multiple cell lineages in vitro and, therefore, they are termed antler stem cells, and antler regeneration is a stem cell-based epimorphic regeneration. Comparisons between the healing process on the stumps from an amputated mouse limb and early regeneration of antlers suggest that the stump of a mouse limb cannot regenerate because of the limited potential of periosteal cells in long bones to proliferate. If we can impart a greater potential of these periosteal cells to proliferate, we might at least be able to partially regenerate limbs lost from humans. Taken together, a greater understanding of the mechanisms that regulate the regeneration of antlers may provide a valuable insight to aid the field of regenerative medicine. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.

Identification of potential bladder progenitor cells in the trigone

Urothelial cells are specialized epithelial cells in the bladder that serve as a barrier toward excreted urine. The urothelium consists of superficial cells (most differentiated cells), intermediate cells, and basal cells; the latter have been considered as urothelium progenitor cells. In this study, BrdU or EdU was administrated to pregnant mice during E8-E13 for 2 consecutive days when bladder development occurs. The presence of label retaining cells was investigated in bladders from offspring. In 6 months old mice ~1% of bladder cells retained labeling. Stem cell markers as defined for other tissues (e.g., p63, CD44, CD117, trop2) co-localized or were in close vicinity to label retaining cells, but they were not uniquely limited to these cells. Remarkably, label retaining cells were distributed in all three cell layers (p63+, CK7+, and CK20+) of the urothelium and concentrated in the bladder trigone. This study demonstrates that bladder progenitor cells are present in all cell layers and reside mostly in the trigone. Understanding the geographic location of slow cycling cells provides crucial information for tissue regenerative purposes in the future.

Mesenchymal stem cell therapy and acute graft-versus-host disease: a review

Mesenchymal stem cells (MSCs) are being widely studied as potential cell therapy agents due to their immunomodulatory properties, which have been established by in vitro studies and in several clinical trials. Within this context, mesenchymal stem cell therapy appears to hold substantial promise, particularly in the treatment of conditions involving autoimmune and inflammatory components. Nevertheless, many research findings are still contradictory, mostly due to difficulties in characterization of the effects of MSCs in vivo. The purpose of this review is to report the mechanisms underlying mesenchymal stem cell therapy for acute graft-versus-host disease, particularly with respect to immunomodulation, migration, and homing, as well as report clinical applications described in the literature.

Prostate progenitor cells proliferate in response to castration

Androgen-deprivation is a mainstay of therapy for advanced prostate cancer but tumor regression is usually incomplete and temporary because of androgen-independent cells in the tumor. It has been speculated that these tumor cells resemble the stem/progenitor cells of the normal prostate. The purpose of this study was to examine the response of slow-cycling progenitor cells in the adult mouse prostate to castration. Proliferating cells in the E16 urogenital sinus were pulse labeled by BrdU administration or by doxycycline-controlled labeling of the histone-H2B GFP mouse. A small population of labeled epithelial cells in the adult prostate localized at the junction of the prostatic ducts and urethra. Fluorescence-activated cell sorting (FACS) showed that GFP label-retaining cells were enriched for cells co-expressing stem cell markers Sca-1, CD133, CD44 and CD117 (4- marker cells; 60-fold enrichment). FACS showed, additionally, that 4-marker cells were androgen receptor positive. Castration induced proliferation and dispersal of E16 labeled cells into more distal ductal segments. When naïve adult mice were administered BrdU daily for 2 weeks after castration, 16% of 4-marker cells exhibited BrdU label in contrast to only 6% of all epithelial cells (P<0.01). In sham-castrated controls less than 4% of 4-marker cells were BrdU labeled (P<0.01). The unexpected and admittedly counter-intuitive finding that castration induced progenitor cell proliferation suggests that androgen deprivation therapy in men with advanced prostate cancer could not only exert pleiotrophic effects on tumor sub-populations but may induce inadvertent expansion of tumor stem cells.

IL-4 induces columnar-like differentiation of esophageal squamous epithelium through JAK/PI3K pathway: possible role in pathogenesis of Barrett's esophagus

Barrett's esophagus is characterized by a distinct Th2-predominant cytokine profile (IL-4) from in vivo or ex vivo evidence. The detailed role of cytokines in Barrett's esophagus, particularly whether Th2 cytokines are causative factors driving metaplastic processes, remains unknown. In this study, air-liquid interface-cultured human esophageal epithelial cells were stimulated by a Th2 cytokine, IL-4, and Th1 cytokines, TNF-α and IL-1β, continuously for 10 days. Barrier function was determined by transepithelial electrical resistance. Morphological changes were investigated by hematoxylin and eosin staining. Keratin profile (keratin 7, 8, 13, and 14) and squamous differentiation markers (involucrin) were investigated by RT-quantitative PCR, Western blotting, and immunohistochemical staining. Pharmacological inhibitors were used to identify the underlying cellular signaling. We report that IL-4, TNF-α, and IL-1β decrease barrier function, but only IL-4 significantly increases cell layers and changes cell morphology. IL-4 time dependently downregulates the expression levels of the squamous cell markers involucrin and keratin 13 and upregulates the expression levels of the columnar cell markers keratin 7 and 8. Neither TNF-α nor IL-1β shows any effect on these indexes. JAK inhibitor I and PI3K inhibitors significantly block the IL-4-induced changes in the levels of keratin 8 and 13. In conclusion, IL-4 inhibits squamous differentiation program of esophageal epithelial cells and induces differentiation toward columnar cells through the JAK/PI3K pathway. Thus IL-4 may be involved in the early stages of Barrett's esophagus development.

Various methods for isolation of multipotent human periodontal ligament cells for regenerative medicine

Periodontal ligament (PDL) is a specialized connective tissue that connects cementum and alveolar bone to maintain and support the teeth in situ and preserve tissue homeostasis. Recent studies have revealed the existence of stem cells in human dental tissues including periodontal ligament that play an important role, not only in the maintenance of the periodontium but also in promoting periodontal regeneration. In this study, human periodontal ligament cells (hPDLCs) were isolated by outgrowth and enzymatic dissociation methods. Expression of surface markers on PDLCs as human mesenchymal stem cells (MSCs) was identified by flow cytometry. In addition, proliferation and differentiation capacity of cultured cells to osteoblasts, adipocytes were evaluated. As a result, we successfully cultured cells from the human periodontal ligament tissues. PDLCs express mesenchymal stem cell (MSC) markers such as CD44, CD73, and CD90 and do not express CD34, CD45, and HLA-DR. PDLCs also possess the multipotential to differentiate into various types of cells, such as osteoblast and adipocytes, in vitro. Therefore, these cells have high potential to serve as materials for tissue engineering, especially dental tissue engineering.

Clinical impact of circulating CD34-positive cells on bone regeneration and healing

Failures in fracture healing after conventional autologous and allogenic bone grafting are mainly due to poor vascularization. To meet the clinical demand, recent attentions in the regeneration and repair of bone have been focused on the use of stem cells such as bone marrow mesenchymal stem cells and circulating skeletal stem cells. Circulating stem cells are currently paid a lot of attention due to their ease of clinical setting and high potential for osteogenesis and angiogenesis. In this report, we focus on the first proof-of-principle experiments demonstrating the collaborative characteristics of circulating CD34(+) cells, known as endothelial and hematopoietic progenitor cell-rich population, which are capable to differentiate into both endothelial cells and osteoblasts. Transplantation of circulating CD34(+) cells provides a favorable environment for fracture healing via angiogenesis/vasculogenesis and osteogenesis, finally leading to functional recovery from fracture. Based on a series of basic studies, we performed a phase 1/2 clinical trial of autologous CD34(+) cell transplantation in patients with tibial or femoral nonunions and reported the safety and efficacy of this novel therapy. In this review, the current concepts and strategies in circulating CD34(+) cell-based therapy and its potential applications for bone repair will be highlighted.

Potential uses, limitations, and basic procedures of micronuclei and nuclear abnormalities in buccal cells

The use of biomarkers as tools to evaluate genotoxicity is increasing recently. Methods that have been used previously to evaluate genomic instability are frequently expensive, complicated, and invasive. The micronuclei (MN) and nuclear abnormalities (NA) technique in buccal cells offers a great opportunity to evaluate in a clear and precise way the appearance of genetic damage whether it is present as a consequence of occupational or environmental risk. This technique is reliable, fast, relatively simple, cheap, and minimally invasive and causes no pain. So, it is well accepted by patients; it can also be used to assess the genotoxic effect derived from drug use or as a result of having a chronic disease. Furthermore the beneficial effects derived from changes in life style or taking additional supplements can also be evaluated. In the present paper, we aim to focus on the explanation of MN test and its usefulness as a biomarker; we further give details about procedures to perform and interpret the results of the test and review some factors that could have an influence on the results of the technique.

Reprogramming for cardiac regeneration

Treatment of cardiovascular diseases remains challenging considering the limited regeneration capacity of the heart muscle. Developments of reprogramming strategies to create in vitro and in vivo cardiomyocytes have been the focus point of a considerable amount of research in the past decades. The choice of cells to employ, the state-of-the-art methods for different reprogramming strategies, and their promises and future challenges before clinical entry, are all discussed here.

Exploiting human CD34+ stem cell-conditioned medium for tissue repair

Despite the progress in our understanding of genes essential for stem cell regulation and development, little is known about the factors secreted by stem cells and their effect on tissue regeneration. In particular, the factors secreted by human CD34+ cells remain to be elucidated. We have approached this challenge by performing a cytokine/growth factor microarray analysis of secreted soluble factors in medium conditioned by adherent human CD34+ cells. Thirty-two abundantly secreted factors have been identified, all of which are associated with cell proliferation, survival, tissue repair, and wound healing. The cultured CD34+ cells expressed known stem cell genes such as Nanog, Oct4, Sox2, c-kit, and HoxB4. The conditioned medium containing the secreted factors prevented cell death in liver cells exposed to liver toxin in vitro via inhibition of the caspase-3 signaling pathway. More importantly, in vivo studies using animal models of liver damage demonstrated that injection of the conditioned medium could repair damaged liver tissue (significant reduction in the necroinflammatory activity), as well as enable the animals to survive. Thus, we demonstrate that medium conditioned by human CD34+ cells has the potential for therapeutic repair of damaged tissue in vivo.

Stem cell transplantation in noise induced hearing loss

OBJECTIVE

To investigate efficacy of bone marrow stem cell implantation in rehabilitation of noise induced hearing loss in rats.

MATERIALS AND METHODS

Hearing loss was induced in male rats by a continuous wide-band noise (8-16 kHz/120 dB/120 min). Ten microliter of stem cell containing solution was injected by a Hamilton syringe with 30 G needle through the round window membrane. Hearing status was examined by, distortion product otoacoustic emissions using DP-OAE. Animals were studied in 4 different groups: (1) Normal hearing animals, undergoing sham surgery (no injection done, only round window membrane ruptured and sealed). (2) Deaf animals, undergoing sham surgery. (3) Deaf animals undergoing surgery and injection of solvent (artificial perilymph). (4) Deaf animals undergoing surgery and injection of artificial perilymph containing BMSCs.

RESULTS

DP-Gram in rat with normal hearing undergoing sham surgery show that procedure has neither negative impact on normal cochlear nor on deaf cochleas. No significant difference (p=0.25) between ears excludes artificial perilymph as a confounding factor. There is no significant difference between ears in animals receiving BMSCs.

CONCLUSIONS

Implanted cells with normal histologic structures have no physiologic function and hearing rehabilitation. Further studies by monitoring the survival of these cells with histologic and appropriate biomarkers will help to investigate differentiation process of these cells.

Homeostatic epithelial renewal in the gut is required for dampening a fatal systemic wound response in Drosophila

Effective defense responses involve the entire organism. To maintain body homeostasis after tissue damage, a systemic wound response is induced in which the response of each tissue is tightly orchestrated to avoid incomplete recovery or an excessive, damaging response. Here, we provide evidence that in the systemic response to wounding, an apoptotic caspase pathway is activated downstream of reactive oxygen species in the midgut enterocytes (ECs), cells distant from the wound site, in Drosophila. We show that a caspase-pathway mutant has defects in homeostatic gut cell renewal and that inhibiting caspase activity in fly ECs results in the production of systemic lethal factors after wounding. Our results indicate that wounding remotely controls caspase activity in ECs, which activates the tissue stem cell regeneration pathway in the gut to dampen the dangerous systemic wound reaction.

Increased expression of endothelin-1 and endothelin receptor A in reflux esophagitis and Barrett's esophagus

Barrett's esophagus (BE) is considered a complication of the inflammation provoked by acid and bile reflux. Endothelin-1 (ET-1) expresses in various cells during inflammatory process. However, the role of ET-1 in human inflamed and uninflamed esophageal tissue is unknown. The present study aimed to examine the expression of ET-1 and its receptors in human reflux esophagitis (RE) and BE. Endoscopic biopsies of normal squamous epithelium (NSE) (n = 20), RE (n = 22), and long segment BE (n = 14) were obtained. The segmental degree of endoscopic and histopathological inflammation was graded, and immunohistochemistry and real-time quantitative polymerase chain reaction were used to determine the expression of ET-1 and endothelin receptor A (ET(A)R) and endothelin receptor B (ET(B)R). ET-1 and ET(A)R messenger RNA (mRNA) levels were higher in RE than in NSE (3.25 ± 1.78 vs. 1.10 ± 0.71, P = 0.000; 2.13 ± 1.06 vs. 1.12 ± 0.64, P = 0.001, respectively). In BE, relative ET-1 mRNA levels in the proximal segment were higher than in the distal segment (3.03 ± 1.83 vs. 1.16 ± 0.70, P = 0.004) and in normal esophageal epithelium (P = 0.002). There was no significantly difference of ET(A)R mRNA levels between the proximal segment and the distal segment (1.99 ± 1.28 vs. 1.14 ± 0.67, P = 0.072). ET(B)R mRNA expression was unaltered between the groups. Furthermore, immunohistochemistry demonstrated that ET-1 expression increased significantly in RE (51.18 ± 30.14) compared with those in NSE (21.10 ± 18.17, P = 0.000) and in distal BE segment (28.02 ± 24.92, P = 0.022). There were more ET-1 positive cells in proximal BE segment (50.07 ± 25.88) than in distal BE segment (P = 0.030) and in NSE (P = 0.001). ET-1 expression increased in a stepwise manner with the growing degree of inflammation, and there were significant differences between mild, moderate, and marked degree esophagitis (36.08 ± 27.84, 65.86 ± 11.82, 98.00 ± 8.49, P = 0.003, respectively). However, expression of receptors remained unchanged. This study demonstrates that over-expression of ET-1 and ET(A)R in esophagitis may be related to the inflammatory process. ET-1 may play a significant role in the progression of Barrett's metaplasia.

Anti-inflammatory role and immunomodulation of mesenchymal stem cells in systemic joint diseases: potential for treatment

INTRODUCTION

Mesenchymal stem cells (MSCs) are multipotent stromal cells characterized by their ability to differentiate into adipocytes, chondrocytes, osteocytes and a number of other lineages. Investigation into their use has increased in recent years as characterization of their immunomodulatory properties has developed, and their role in the pathophysiology of joint disease has been suggested.

AREAS COVERED

MSCs demonstrate immunosuppressive functionality by suppressing T- and B-cell responses following activation by cytokines such as IL-6 and IL-1α. They also can be induced to exert pro-inflammatory effects in the presence of acute inflammatory environment due to the actions of TNF-α and IFN-γ. In inflammatory joint diseases such as rheumatoid arthritis, MSCs in bone marrow migrate to joints by a TNF-α-dependent mechanism and may be in part responsible for the disease process. MSCs have also been demonstrated in increased numbers in periarticular tissues in osteoarthritis, which may reflect an attempt at joint regeneration.

EXPERT OPINION

Clinical applications for MSCs have shown promise in a number of inflammatory and autoimmune disorders. Future work is likely to further reveal the immunosuppressive characteristics of MSCs, their role in the pathophysiology of joint diseases and provide the basis for new avenues for treatment.

Perivascular mesenchymal stem cells in the adult human brain: a future target for neuroregeneration?

Perivascular adult stem cells have been isolated from several tissues, including the adult human brain. They have unique signatures resembling both pericytes and mesenchymal stem cells. Understanding the nature of these cells in their specific vascular niches is important to determine their clinical potential as a new adult stem cell source. Indeed, they have promising features in vitro in terms of multipotency, immunomodulation and secretion of growth factors and cytokines. However, their in vivo function is less known as yet. Recent emerging data show a crucial role of perivascular mesenchymal stem cells in tissue homeostasis and repair. Furthermore, these cells may play an important role in adult stem cell niche regulation and in neurodegeneration. Here we review the recent literature on perivascular mesenchymal stem cells, discuss their different in vitro functions and highlight especially the specific properties of brain-derived perivascular mesenchymal stem cells. We summarize current evidence that suggests an important in vivo function of these cells in terms of their regenerative potential that may indicate a new target cell for endogenous tissue regeneration and repair.

MicroRNA-181a* Targets Nanog in a Subpopulation of CD34(+) Cells Isolated From Peripheral Blood

Exploiting the properties of stem cells by microRNA (miRNA) profiling offers an attractive approach to identify new regulators of stem cell fate. Although numerous miRNA have been screened from hematopoietic stem cells (HSC), the targets corresponding to many of these miRNA have not yet been fully elucidated. By miRNA profiling in a subpopulation of CD34+ cells isolated from peripheral blood, we have identified eight clusters of miRNA that were differentially expressed. Further analysis of one of the clusters by bioinformatics revealed that a miRNA, miR-181a*, which is highly expressed in the adherent CD34+ cells, affects the expression levels of Nanog, a stem cell surrogate marker. We show specifically by reporter assay and mutational analysis that miR-181a* targets a seedless 3′ compensatory site in the 3′UTR of Nanog and affects gene expression. We demonstrate that inhibiting miR-181a* upregulates the Nanog expression level, in addition to an increase in alkaline phosphatase activity. Our studies suggest that miR-181a* may be important in controlling the expression level of Nanog in a subpopulation of CD34+ cells.

TGF-β and stem cell factor regulate cell proliferation in the proximal stem cell niche

BACKGROUND

Stem cells are located in specific regulatory environments termed niches, which modulate the survival and proliferation of the cells through a variety of both mitogenic and inhibitory cytokines. In the murine prostate, stem cells are located in the proximal region of prostatic ducts. We examined the regulation of murine prostate cells in the stem cell niche by transforming growth factor beta (TGF-β) and stem cell factor (SCF).

METHODS

Prostate cells from the proximal and distal regions of prostatic ducts were cultured in the presence and absence of TGF-β and SCF, both on collagen-coated wells and in collagen gels. Cell growth on collagen was assessed by determining cell number. Cell growth in collagen gels was quantified by determining the number, size and complexity of prostatic ducts. The basal and luminal phenotype of the cells was determined by immunohistochemistry.

RESULTS

Endogenous TGF-β inhibited proliferation and promoted differentiation of proximal cells towards a luminal phenotype. It also inhibited duct-forming capacity and promoted differentiation of prostatic ducts towards a luminal phenotype. Addition of SCF enhanced proximal cell proliferation on collagen-coated wells and duct formation in collagen gels. Proliferation was further increased by ablation of endogenous TGF-β.

CONCLUSION

Proliferation and the basal/luminal cell composition of cells isolated from the proximal region of prostatic ducts, the stem cell niche, is regulated in part by opposing effects of SCF and endogenous TGF-β.

Local microenvironment provides important cues for cell differentiation in lingual epithelia

Transgenic Keratin14-rtTA-PTR mice specifically express Keratin14 (K14) in the tongue epithelia, as well as co-express EGFP and the dominant negative ΔTgfbr2 genes upon treatment with Doxycycline (Dox). As TGF-β signaling negatively regulates the stem cell cycle and proliferation, its disruption by Dox induction in these transgenic mice shortens the cell cycle and allows observation of the final fate of those mutated cell lineages within a short period of time. Here, we used inducible transgenic mice to track the K14+ cells through the cell migration stream by immunohistochemical an immunofluorescent imaging. We showed that these cells have different development patterns from the tip to posterior of the tongue, achieved presumably by integrating positional information from the microenvironment. The expression of the K14 gene was variable, depending on the location of the tongue and papillae. Disruption of TGF-β signaling in K14+ progenitor cells resulted in proliferation of stem cell pools.

Optimality in the development of intestinal crypts

Intestinal crypts in mammals are comprised of long-lived stem cells and shorter-lived progenies. These two populations are maintained in specific proportions during adult life. Here, we investigate the design principles governing the dynamics of these proportions during crypt morphogenesis. Using optimal control theory, we show that a proliferation strategy known as a "bang-bang" control minimizes the time to obtain a mature crypt. This strategy consists of a surge of symmetric stem cell divisions, establishing the entire stem cell pool first, followed by a sharp transition to strictly asymmetric stem cell divisions, producing nonstem cells with a delay. We validate these predictions using lineage tracing and single-molecule fluorescence in situ hybridization of intestinal crypts in infant mice, uncovering small crypts that are entirely composed of Lgr5-labeled stem cells, which become a minority as crypts continue to grow. Our approach can be used to uncover similar design principles in other developmental systems.

Radiation-induced carcinogenesis: mechanistically based differences between gamma-rays and neutrons, and interactions with DMBA

Different types of ionizing radiation produce different dependences of cancer risk on radiation dose/dose rate. Sparsely ionizing radiation (e.g. γ-rays) generally produces linear or upwardly curving dose responses at low doses, and the risk decreases when the dose rate is reduced (direct dose rate effect). Densely ionizing radiation (e.g. neutrons) often produces downwardly curving dose responses, where the risk initially grows with dose, but eventually stabilizes or decreases. When the dose rate is reduced, the risk increases (inverse dose rate effect). These qualitative differences suggest qualitative differences in carcinogenesis mechanisms. We hypothesize that the dominant mechanism for induction of many solid cancers by sparsely ionizing radiation is initiation of stem cells to a pre-malignant state, but for densely ionizing radiation the dominant mechanism is radiation-bystander-effect mediated promotion of already pre-malignant cell clone growth. Here we present a mathematical model based on these assumptions and test it using data on the incidence of dysplastic growths and tumors in the mammary glands of mice exposed to high or low dose rates of γ-rays and neutrons, either with or without pre-treatment with the chemical carcinogen 7,12-dimethylbenz-alpha-anthracene (DMBA). The model provides a mechanistic and quantitative explanation which is consistent with the data and may provide useful insight into human carcinogenesis.