The presence of ABCG2-dependent side population cells in human periodontal ligaments

ABCG2 is a selectable marker for enhanced multilineage differentiation potential in periodontal ligament stem cells

Periodontal ligament stem cells (PDLSCs) provide an important source for tissue regeneration and may become especially useful in the formation of osteogenic seeds. PDLSCs can be cultured, expanded, and differentiated in vitro; thus, they may be applied in the long-term treatment of the defects in the dental regions. Here we studied numerous potential markers allowing the selection of human PDLSCs with a maximum differentiation potential. We followed the expression of the ATP-binding cassette subfamily G member 2 (ABCG2) membrane transporter protein and isolated ABCG2-expressing cells by using a monoclonal antibody, recognizing the transporter at the cell surface in intact cells. The expression of the ABCG2 protein, corresponding to the so-called side-population phenotype in various tissue-derived stem cells, was found to be a useful marker for the selection of PDLSCs with enhanced osteogenic, chondrogenic, and adipogenic differentiation. These findings may have important applications in achieving efficient dental tissue regeneration by using stem cells from extracted teeth.

Enhanced Bone-Forming Activity of Side Population Cells in the Periodontal Ligament

Regeneration of alveolar bone is critical for the successful treatment of periodontal diseases. The periodontal ligament (PDL) has been widely investigated as a source of cells for the regeneration of periodontal tissues. In the present study where we attempted to develop an effective strategy for alveolar bone regeneration, we examined the osteogenic potential of side population (SP) cells, a stem cell-containing population that has been shown to be highly abundant in several kinds of tissues, in PDL cells. Isolated SP cells from the rat PDL exhibited a superior ability to differentiate into osteoblastic cells compared with non-SP (NSP) and unsorted PDL cells in vitro. The mRNA expressions of osteoblast markers and bone morphogenetic protein (BMP) 2 were significantly upregulated in SP cells and were further increased by osteogenic induction. To examine the bone-forming activity of SP cells in vivo, PDL SP cells isolated from green fluorescent protein (GFP)-transgenic rats were transplanted with hydroxyapatite (HA) disks into wild-type animals. SP cells exhibited a high ability to induce the mineralized matrix compared with NSP and unsorted PDL cells. At 12 weeks after the implantation, some of the pores in the HA disks with SP cells were filled with mineralized matrices, which were positive for bone matrix proteins, such as osteopontin, bone sialoprotein, and osteocalcin. Furthermore, osteoblast- and osteocyte-like cells on and in the bone-like mineralized matrices were GFP positive, suggesting that the matrices were directly formed by the transplanted cells. These results suggest that PDL SP cells possess enhanced osteogenic potential and could be a potential source for cell-based regenerative therapy for alveolar bone.

IMD-0354 targets breast cancer stem cells: a novel approach for an adjuvant to chemotherapy to prevent multidrug resistance in a murine model

Although early detection of breast cancer improved in recent years, prognosis of patients with late stage breast cancer remains poor, mostly due to development of multidrug resistance (MDR) followed by tumor recurrence. Cancer stem cells (CSCs), with higher drug efflux capability and other stem cell-like properties, are concentrated in a side population (SP) of cells, which were proposed to be responsible for MDR and tumor repopulation that cause patients to succumb to breast cancer. Therefore, targeting of CSCs as an adjuvant to chemotherapy should be able to provide a more effective treatment of this disease. Here, we used IMD-0354, an inhibitor of NF-κB, identified for targeting CSCs, in a combination therapy with doxorubicin encapsulated in targeted nanoparticles. IMD-0354 did target CSCs, evidenced by a decrease in the SP, demonstrated by the inhibition of the following: dye/drug efflux, reduction in ABC transporters as well as in colony formation in soft agar and low attachment plates. Decrease of stem-like gene expression of Oct4, Nanog and Sox2, and apoptosis resistance related to the Survivin gene also was observed after treatment with this compound. In addition, IMD-0354 targeted non-CSCs as indicated by reducing viability and increasing apoptosis. Targeted drug delivery, achieved with a legumain inhibitor, proved to enhance drug delivery under hypoxia, a hallmark of the tumor microenvironment, but not under normoxia. Together, this allowed a safe, non-toxic delivery of both anticancer agents to the tumor microenvironment of mice bearing syngeneic metastatic breast cancer. Targeting both bulk tumor cells with a chemotherapeutic agent and CSCs with IMD-0354 should be able to reduce MDR. This could eventually result in decreasing tumor recurrences and/or improve the outcome of metastatic disease.

Cardiac side population cells: moving toward the center stage in cardiac regeneration

Over the past decade, extensive work in animal models and humans has identified the presence of adult cardiac progenitor cells, capable of cardiomyogenic differentiation and likely contributors to cardiomyocyte turnover during normal development and disease. Among cardiac progenitor cells, there is a distinct subpopulation, termed "side population" (SP) progenitor cells, identified by their unique ability to efflux DNA binding dyes through an ATP-binding cassette transporter. This review highlights the literature on the isolation, characterization, and functional relevance of cardiac SP cells. We review the initial discovery of cardiac SP cells in adult myocardium as well as their capacity for functional cardiomyogenic differentiation and role in cardiac regeneration after myocardial injury. Finally, we discuss recent advances in understanding the molecular regulators of cardiac SP cell proliferation and differentiation, as well as likely future areas of investigation required to realize the goal of effective cardiac regeneration.

Flow cytometry in cancer stem cell analysis and separation

In recent years, a special type of cancer cell--the cancer stem cell (CSC)--has been identified and characterized for different tumors. CSCs may be responsible for the recurrence of a tumor following a primarily successful therapy and are thought to bear a high metastatic potential. For the development of efficient treatment strategies, the establishment of reliable methods for the identification and effective isolation of CSCs is imperative. Similar to their stem cell counterparts in bone marrow or small intestine, different cluster of differentiation surface antigens have been characterized, thus enabling researchers to identify them within the tumor bulk and to determine their degree of differentiation. In addition, functional properties characteristic of stem cells can be measured. Side population analysis is based on the stem cell-specific activity of certain ATP-binding cassette transporter proteins, which are able to transport fluorescent dyes out of the cells. Furthermore, the stem cell-specific presence of aldehyde dehydrogenase isoform 1 can be used for CSC labeling. However, the flow cytometric analysis of these CSC functional features requires specific technical adjustments. This review focuses on the principles and strategies of the flow cytometric analysis of CSCs and provides an overview of current protocols as well as technical requirements and pitfalls. A special focus is set on side population analysis and analysis of ALDH activity. Flow cytometry-based sorting principles and future flow cytometric applications for CSC analysis are also discussed.

Notch signalling pathway in tooth development and adult dental cells

Notch signalling is a highly conserved intercellular signal transfer mechanism that includes canonical and non-canonical pathways. It regulates differentiation and proliferation of stem/progenitor cells by means of para-inducing effects. Expression and activation of Notch signalling factors (receptors and ligands) are critical not only for development of the dental germ but also for regeneration of injured tissue associated with mature teeth. Notch signalling plays key roles in differentiation of odontoblasts and osteoblasts, calcification of tooth hard tissue, formation of cusp patterns and generation of tooth roots. After tooth eruption, Notch signalling can also be triggered in dental stem cells of the pulp, where it induces them to differentiate into odontoblasts, thus generating fresh dentine tissue. Other signalling pathways, such as TGFβ, NF-κB, Wnt, Fgf and Shh also interact with Notch signalling during tooth development.

Mesenchymal stem cell properties of periodontal ligament cells from deciduous and permanent teeth

BACKGROUND

Human postnatal stem cells have been identified in periodontal ligaments (PDLs). In this study, the in vitro biologic properties of CD105(+) enriched cell subsets from PDLs harvested from deciduous (DePDL) and permanent (PePDL) teeth are comparatively assessed.

METHODS

PDL tissue was obtained from 12 teeth (six primary and six permanent) from which CD105(+) CD34(-) CD45(-) cells were isolated by magnetic cell sorting. To identify and quantitatively compare the stem cell markers, DePDL and PePDL cells were assessed for CD166 surface antigen expression by flow cytometry, real-time polymerase chain reaction, and immunostaining for Stro-1 and Oct-4, osteogenic and adipogenic differentiation, and proliferation rate by trypan blue method.

RESULTS

Magnetic cell sorting isolated cell populations containing 23.87% (+/- 11.98%) and 11.68% (+/- 6.27%) of CD105(+) expressing cells from PePDL and DePDL, respectively. Flow cytometric analysis demonstrated a higher proportion of CD105(+) cells coexpressing CD166 surface antigen in PePDL, whereas immunostaining and real-time polymerase chain reaction analysis demonstrated that both cell subsets expressed Stro-1 and Oct-4. DePDL-CD105(+) subsets were more proliferative compared to PePDL subsets, and both cell populations showed multipotential capabilities to differentiate in vitro to osteoblast/cementoblast- and adipocyte-like cells. However, a higher expression of adipogenic-related genes was observed in DePDL cells, whereas PePDL-CD105(+) cell subset presented a more homogeneous osteoblast/cementoblast response.

CONCLUSION

These findings demonstrate that highly purified mesenchymal progenitor cell subsets can be obtained from the PDLs of both deciduous and permanent teeth, and further indicate phenotype dissimilarities that may have an impact on their clinical applications.

Analysis of side population cells derived from dental pulp tissue

AIM

To investigate the characteristics of side population (SP) cells derived from the dental pulp of young and aged rats.

METHODOLOGY

Maxillary and mandibular incisors were extracted from 5-week-old (young) rats and 60- to 80-week-old (aged) rats. Coronal pulp tissue was removed mechanically, and single-cell suspensions were prepared using collagenase and dispase. Cells were stained with Hoechst 33342 and sorted with an fluorescence-activated cell sorter (FACS). Isolated SP and main population (MP) cells were analysed by real-time reverse transcription polymerase chain reaction, immunohistochemical localization and cell cycle determination. Two-way analysis of variance and the multiple comparison Scheffè test were used for statistical analysis (P<0.05).

RESULTS

Approximately 0.40% of pulp cells in young rats and 0.11% in aged rats comprised SP cells. SP cells expressed a higher mRNA level of ATP-binding cassette transporter G2 (ABCG2), but lower mRNA levels of nestin, alkaline phosphatase, p16 and p57 than MP cells in both age groups. Immunohistochemical observation revealed ABCG2-positive cells localized in the cell-rich zone and nestin in the odontoblastic layer in both groups. Furthermore, the majority of both young and aged SP and MP cells were in growth arrest of the G(0) /G(1) phase.

CONCLUSION

The FACS analysis revealed a decrease in the proportion of SP cells with age, whilst p16 mRNA expression indicated an increase in cell senescence. The cell cycles of SP and MP cells from both young and aged dental pulp were generally in the G0/G1 phase.

In vitro neural/glial differentiation potential of periodontal ligament stem cells

INTRODUCTION

It is known that periodontal ligament stem cells (PDLSCs) can differentiate into cementoblast-like cells, adipocytes and collagen-forming cells. However, whether PDLSCs are able to differentiate into Schwann cells and which method is best for their neural induction remain unknown. We attempted to determine whether PDLSCs possessed the potential for neural differentiation in vitro.

MATERIALS AND METHODS

We isolated and multiplied PDLSCs from periodontal ligaments obtained from the teeth (n = 24) of 8-month-old beagle dogs. Four protocols with different chemicals and growth factors were adopted to induce the PDLSCs to differentiate into Schwann cells. Immunochemistry, RT-PCR and qRT-PCR were performed to investigate the in vitro neural differentiation potential of PDLSCs.

RESULTS

We compared the 4 different protocols and showed that all 4 protocols could successfully induce PDLSCs to express nestin, GFAP and S100, markers for Schwann cells. Further, qRT-PCR revealed relative differences in the expression levels of these 3 genes in differentiated PDLSCs obtained by different protocols.

CONCLUSIONS

We conclude that PDLSCs have neural/glial differentiation potential in vitro and that neural/glial differentiation can be induced in PDLSCs if suitable protocols are followed. We also found that supplementing the growth medium with suitable growth factors is more effective than applying chemicals alone. While nerve growth factor is more effective than platelet-derived growth factor for inducing neural/glial differentiation in PDLSCs, pre-induction of PDLSCs with dimethyl sulphoxide yields better results than those obtained with all-trans-retinoic acid.

The presence of a side population and its marker ABCG2 in human deciduous dental pulp cells

Stem cells have been identified using the DNA-binding dye Hoechst 33342 and flow cytometry (FCM) in various tissues known as the side population (SP). The present study shows, for the first time, the presence of side population cells in human deciduous dental pulp cells (DPCs). Flow cytometric identification revealed that 2% of human deciduous DPCs were SP cells and that this SP profile disappeared in the presence of verapamil. The SP marker ABCG2 protein was localized to DPCs in the cell membrane by immunofluorescence staining, and flow cytometric analysis demonstrated that 3.6% of DPCs were ABCG2-positive. Furthermore, quantitative real-time PCR proved that ABCG2 mRNA expression in DPCs isolated from human exfoliated deciduous teeth was higher than in DPCs from permanent teeth. Our findings demonstrate that DPCs from human exfoliated deciduous teeth contain a higher proportion of the SP phenotype than permanent teeth and that they may constitute a stem cell population.

Periodontal tissue engineering and regeneration: current approaches and expanding opportunities

The management of periodontal tissue defects that result from periodontitis represents a medical and socioeconomic challenge. Concerted efforts have been and still are being made to accelerate and augment periodontal tissue and bone regeneration, including a range of regenerative surgical procedures, the development of a variety of grafting materials, and the use of recombinant growth factors. More recently, tissue-engineering strategies, including new cell- and/or matrix-based dimensions, are also being developed, analyzed, and employed for periodontal regenerative therapies. Tissue engineering in periodontology applies the principles of engineering and life sciences toward the development of biological techniques that can restore lost alveolar bone, periodontal ligament, and root cementum. It is based on an understanding of the role of periodontal formation and aims to grow new functional tissues rather than to build new replacements of periodontium. Although tissue engineering has merged to create more opportunities for predictable and optimal periodontal tissue regeneration, the technique and design for preclinical and clinical studies remain in their early stages. To date, the reconstruction of small- to moderate-sized periodontal bone defects using engineered cell-scaffold constructs is technically feasible, and some of the currently developed concepts may represent alternatives for certain ideal clinical scenarios. However, the predictable reconstruction of the normal structure and functionality of a tooth-supporting apparatus remains challenging. This review summarizes current regenerative procedures for periodontal healing and regeneration and explores their progress and difficulties in clinical practice, with particular emphasis placed upon current challenges and future possibilities associated with tissue-engineering strategies in periodontal regenerative medicine.

Isolation of multipotent stem cells in human periodontal ligament using stage-specific embryonic antigen-4

The periodontal ligament (PDL) comprises adult stem cells, which are responsible for periodontal tissue regeneration. In the present study, we investigated the specific profile of the stem cells in the human PDL. Microscopic analysis demonstrated that PDL cells showed a fibroblastic appearance, forming flat and loose aggregates. PDL cells expressed embryonic stem cell-associated antigens (SSEA-1, SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, OCT4, NANOG, SOX2, and REX1, and alkaline phosphatase activity), as well as conventional mesenchymal stem cell markers. When PDL cells were cultured in the presence of all-trans-retinoic acid, the numbers of SSEA-3+ and SSEA-4+ PDL cells were significantly decreased, while that of SSEA-1+ was increased. SSEA-4+ PDL cells showed a greater telomere length and growth rate. SSEA-4+ PDL cells exhibited the potential to generate specialized cells derived from three embryonic germ layers: mesodermal (adipocytes, osteoblasts, and chondrocytes), ectodermal (neurons), and endodermal (hepatocytes) lineages. Our findings demonstrated that SSEA-4, a major antigen to distinguish human embryonic stem cells, could also be used to identify multipotent stem cells in the PDL. Hence, SSEA-4+ human PDL cells appear to be a promising source of stem cells for regenerative medicine.

The dog liver contains a "side population" of cells with hepatic progenitor-like characteristics

The aim of this study was to isolate and characterize potential progenitor cells from healthy dog livers. Stem/progenitor cells can be prospectively isolated from a diversity of tissues using their ability to efficiently pump out the dye Hoechst33342, thereby portraying a side population (SP) in dual-wavelength flow cytometry. We here describe the detection of a SP in dog liver, constituting approximately 3 % of the nonparenchymal-enriched cell fractions. A subpopulation of the SP (approximately 30 %) was immunonegative for the panhematopoietic marker CD45, and consisted predominantly of small, mononuclear, keratin 7-immunoreactive cells; characteristics suggestive of a liver progenitor cell phenotype. Both the CD45- and CD45+ SP showed upregulated expression of progenitor/cholangiocyte marker genes, but also low-level expression of hepatocyte markers, suggesting the presence of progenitor cells committed to the hepatic lineage in both SP fractions. Our findings demonstrate that healthy canine liver contains a small population of cells with progenitor-like characteristics that can be isolated on the basis of efficient Hoechst33342 expulsion.

Formation of bone-like mineralized matrix by periodontal ligament cells in vivo: a morphological study in rats

Periodontal ligament (PDL) is a unique connective tissue that not only connects cementum and alveolar bone to support teeth, but also plays an important role in reconstructing periodontal tissues. Previous studies have suggested that PDL cells have osteogenic potential; however, they lack precise histological examinations. Here, we studied bone-like matrix formation by PDL cells in rats using morphological techniques. Rat and human PDL cells exhibited substantial alkaline phosphatase activity and induced mineralization in vitro. RT-PCR analyses showed that PDL cells expressed the osteoblast markers, Runx2, osterix, and osteocalcin. These results suggest that PDL cells share similar phenotypes with osteoblasts. To examine the bone-like matrix formation in vivo, PDL cells isolated from green fluorescent protein (GFP)-transgenic rats were inoculated with hydroxyapatite (HA) disks into wild-type rats. Five weeks after the implantation, the pores in HA disks were occupied by GFP-positive cells. Mineralized matrix formation was also found on the surface of HA pores. At 12 weeks, some of the pores were filled with bone-like mineralized matrices (BLMM), which were positive for the bone matrix proteins, osteopontin, bone sialoprotein, and osteocalcin. Immunohistochemical examination revealed that most of the osteoblast- and osteocyte-like cells on or in the BLMM were GFP-positive, suggesting that the BLMM were directly formed by the inoculated PDL cells. On the pore surfaces, Sharpey's fiber-like structures embedded in cementum-like mineralized layers were also observed. These results collectively suggest that PDL cells have the ability to form periodontal tissues and could be a useful source for regenerative therapies of periodontal diseases.

Investigating a clonal human periodontal ligament progenitor/stem cell line in vitro and in vivo

The lifespan of the tooth is influenced by the periodontal ligament (PDL), a specialized connective tissue that connects the cementum with the tooth socket bone. Generation of a cell line from PDL progenitor/stem cells would allow development of tissue engineering-based regenerative PDL therapy. However, little is known about the characteristics of PDL progenitor/stem cells because PDL tissue consists of a heterogeneous cell population and there are no pure PDL cell lines. Recently, we succeeded in immortalizing primary human PDL fibroblasts (HPLFs) by transfecting them with SV40 T-antigen and hTERT (Cell Tissue Res 2006; 324: 117-125). In this study, we isolated three clonal cell lines from these immortalized cells (lines 1-4, 1-11, and 1-24) that express RUNX-2, Col I, ALP, OPN, OCN, RANKL, OPG, scleraxis, periostin, Col XII, and alpha-SMA mRNA. Immunocytochemical analysis demonstrated that CD146 was expressed in cell lines 1-4 and 1-11 and that STRO-1 was expressed in lines 1-11 and 1-24. Lines 1-4 and 1-11 differentiated into osteoblastic cells and adipocytes when cultured in lineage-specific differentiation media. Four weeks after transplanting cell line 1-11 into immunodeficient mice with beta-tricalcium phosphate (beta-TCP), the transplant produced cementum/bone-like tissues around the beta-TCP. Eight weeks after transplantation, the 1-11 cell transplant formed PDL-like structures on the surface of the beta-TCP. These data suggest that cell line 1-11 was derived from a progenitor/stem cell present in the PDL and should be very useful for studying the biology and regeneration of human periodontium.

Induction of chondrogenesis and superficial zone protein accumulation in synovial side population cells by BMP-7 and TGF-beta1

Synovial cells are known to contain a sub-population of cells with multipotent differentiating capacity including chondrocytes. However, the stem/progenitor cells in synovial cells have not been well characterized. Stem/progenitor cells can exclude Hoechst 33342 dye, and the cell fraction with this property is called "side population (SP)." SP cells are present in many adult tissues. The aim of this investigation was to identify, isolate, and characterize SP cells from bovine synovium. Hoechst dye efflux and fluorescence activated cell sorting showed that synovial cells contained 0.60% SP cells. In the presence of verapamil, an inhibitor of ABC transporters critical for the dye efflux property, the SP cell fraction was not observed, indicating the critical role of ABC transporters. Isoforms of ABC transporters (ABCG2 and ABCB1 mRNA) were highly expressed in SP cells derived from the synovial cells by real-time RT-PCR analysis. Bone morphogenetic protein-7 (BMP-7) induced type II collagen mRNA expression characteristic of chondrogenesis in articular cartilage with both SP and non-SP cells. In addition, expression of SZP mRNA, a marker of the surface layer of articular cartilage, was significantly up-regulated by BMP-7, and the protein accumulation of SZP was stimulated by both BMP-7 and TGF-beta1. Thus, synovial cells contain ABC transporter-dependent SP cells. These findings demonstrate that side population cells of synovium differentiate toward an articular chondrocyte phenotype of the surface layer and have direct implications for tissue engineering and regeneration of articular cartilage.

Side population cells in the human vocal fold

OBJECTIVES

The regenerative processes of the vocal fold, or the existence of stem cells in the folds, are unknown. Side population (SP) cells are defined as cells that have the ability to exclude the DNA binding dye, Hoechst 33342. They are regarded as a cell population enriched with stem cells and can be isolated from non-SP cells by a fluorescence-activated cell sorter. This study was designed to determine whether SP cells exist in the human vocal fold, as a first step in elucidating the regenerative mechanisms of the vocal fold.

METHODS

Seven human excised larynges were used in this study. Two were used for fluorescence-activated cell sorter analysis, and 5 were subjected to immunohistochemical analysis with antibodies against an adenosine triphosphate binding cassette transporter family member, ABCG2, which is expressed in SP cells.

RESULTS

The number of SP cells in the human vocal fold was about 0.2% of the total number of cells. ABCG2-positive cells were identified in both the epithelium and subepithelial tissue throughout the entire vocal fold.

CONCLUSIONS

This preliminary study demonstrated the existence of SP cells in the human vocal fold. Further studies are warranted to clarify how these cells work in the vocal fold, particularly in the regenerative process.

Side population cells expressing ABCG2 in human adult dental pulp tissue

AIM

To investigate the presence of side population (SP) cells by the Hoechst exclusion method in human adult dental pulp tissue.

METHODOLOGY

Human adult dental pulp-derived cells were generated from third molar teeth. The cells were stained with Hoechst 33342 and sorted into SP cells or non-SP cells [main population (MP) cells]. Both cell types were compared with cell growth and RT-PCR analyses.

RESULTS

SP cells that express ABCG2, Nestin, Notch-1 and alpha-smooth muscle actin were found at frequencies ranging from 0.67% to 1.02%. This SP profile disappeared in the presence of verapamil. These SP cells expressed dentine sialophosphoprotein and dentine matrix protein-1 when cultured in osteogenic medium.

CONCLUSION

Human adult dental pulp tissue contains SP cells that differentiate into odontoblast-like cells.

Stand der humanen dentalen Stammzellforschung

This review article arranges the current results of stem cell biology for their use in dentistry. There are different types of stem cells, which are applicable for dental treatments. The use of embryonic stem cells, whose possibilities for breeding an artificial tooth were hardly evaluated, is however ethically precarious. On the other side the ethically harmless adult stem cells, which were isolated for example from bone marrow, were little examined for their capability of differentiation into dental tissues. Therefore their forthcoming use in dentistry is rather improbable. However, dental ectomesenchymal stem cells are more promising for dentistry in future. For example dental pulp stem cells (DPSCs) are capable to differentiate into dentin under in vitro conditions. Moreover it is possible to use periodontal ligament (PDL) stem cells and dental follicle precursors for periodontal tissue differentiations in vitro. Recently new populations of stem cells were isolated from the dental pulp and the PDL. These cells distinguish from the initially isolated DPSCs and PDL stem cells in growth and cell differentiation. Therefore stem cell markers are very important for the characterization of dental stem cells. A significant marker for dental stem cells is STRO-1, which is also a marker for bone marrow derived mesenchymal stem cells. Nonetheless dental stem cells are CD45 negative and they express rarely hematopoietic stem cell markers. These research results plead for the participation of dental stem cells in dental practice in future.

Isolation of multipotent stem cells from adult rat periodontal ligament by neurosphere-forming culture system

Adult multipotent stem cells have been isolated from various non-neural tissues. Here, we report the isolation of multipotent stem cells from rat periodontal ligament (PDL) using neurosphere-forming culture system. Enzymatically dissociated PDL cells were cultured in serum-free basal medium containing EGF, bFGF, and LIF. Free-floating spheres expressing nestin, GFAP, and vimentin were formed by 7 days of the culture. In addition, spheres expressed mRNA of neural crest-associated transcription factors Twist, Slug, Sox2, and Sox9. PDL-derived spheres differentiated into multinucleated myotubes, NFM-positive neuron-like cells, GFAP-positive astrocyte-like cells and CNPase-positive oligodendrocyte-like cells. Methylcellulose colony-forming assay revealed that a single PDL cell could form a sphere at a frequency of approximately 0.01% of total cells. These data indicate that PDL-derived spheres contained multipotent adult stem cells capable of differentiating into both neural and mesodermal progeny. This is the first report of the isolation of PDL-derived stem cells with primitive neural crest stem cell features.

Side Population Analysis Using a Violet-Excited Cell-Permeable DNA Binding Dye

Hoechst 33342 side population (SP) analysis is a common method for identifying stem cells in mammalian hematopoietic and nonhematopoietic tissues. Although widely employed for stem cell analysis, this method requires an ultraviolet (UV) laser to excite Hoechst 33342. Flow cytometers equipped with UV sources are not common because of the cost of both the laser and optics that can transmit light UV light. Violet laser sources are inexpensive and are now common fixtures on flow cytometers, but have been previously shown to provide insufficient Hoechst dye excitation for consistent resolution of SP cells. One solution to this problem is to identify additional fluorescent substrates with the same pump specificity as Hoechst 33342, but with better violet excitation characteristics. DyeCycle Violet reagent has emission characteristics similar to those of Hoechst 33342, but with a longer wavelength excitation maxima (369 nm). When this dye is loaded into hematopoietic cells, a sharply resolved side population was also observed, similar in appearance to that seen with Hoechst 33342. Unlike Hoechst SP, DCV SP was similar in appearance with both violet and UV excitation. DCV SP could be inhibited fumitremorgin C, and showed the same membrane pump specificity as Hoechst 33342. Simultaneous immunophenotyping with stem cell markers in mouse bone marrow demonstrated that DCV SP was restricted to the stem cell lineage(-) Sca-1(+) c-kit(+) cells population, as is Hoechst SP. Pending confirmation by functional analysis of DCV SP cells, these results suggest that DCV efflux identified approximately the same stem cell population as did Hoechst 33342 efflux. Substituting DCV for Hoechst 33342 in the SP technique may, therefore, allow side population analysis on flow cytometers with violet lasers.

Physiological features of periodontal regeneration and approaches for periodontal tissue engineering utilizing periodontal ligament cells

Experimental studies have shown that the potential of periodontal regeneration seems to be limited by the regenerative capacity of the cells involved. The regeneration of damaged periodontal tissues is mediated by various periodontal cells and is regulated by a vast array of extracellular matrix informational molecules that induce both selective and nonselective responses in different cell lineages and their precursors. In this paper, we first review periodontal ligament tissue and its different cell subpopulations including fibroblasts and paravascular stem cells, and their functions during the development and homeostasis of periodontal tissues. Because conventional periodontal regeneration methods remain insufficient to obtain a complete and reliable periodontal regeneration, the concept of periodontal tissue engineering has been based on the generation of the conditions necessary to improve the healing of periodontal tissues. Additionally, the potential of periodontal ligament cells for use in periodontal tissue engineering to overcome the limitations of conventional periodontal regenerative therapies is discussed, followed by an update of the recent progress and future directions of research utilizing periodontal ligament cells for predictable periodontal regeneration.

Human cardiac stem cells exhibit mesenchymal features and are maintained through Akt/GSK-3beta signaling

Recent evidence suggested that human cardiac stem cells (hCSCs) may have the clinical application for cardiac repair; however, their characteristics and the regulatory mechanisms of their growth have not been fully investigated. Here, we show the novel property of hCSCs with respect to their origin and tissue distribution in human heart, and demonstrate the signaling pathway that regulates their growth and survival. Telomerase-active hCSCs were predominantly present in the right atrium and outflow tract of the heart (infant > adult) and had a mesenchymal cell-like phenotype. These hCSCs expressed the embryonic stem cell markers and differentiated into cardiomyocytes to support cardiac function when transplanted them into ischemic myocardium. Inhibition of Akt pathway impaired the hCSC proliferation and induced apoptosis, whereas inhibition of glycogen synthase kinase-3 (GSK-3) enhanced their growth and survival. We conclude that hCSCs exhibit mesenchymal features and that Akt/GSK-3beta may be crucial modulators for hCSC maintenance in human heart.

ABC transporters, neural stem cells and neurogenesis – a different perspective

Stem cells intrigue. They have the ability to divide exponentially, recreate the stem cell compartment, as well as create differentiated cells to generate tissues. Therefore, they should be natural candidates to provide a renewable source of cells for transplantation applied in regenerative medicine. Stem cells have the capacity to generate specific tissues or even whole organs like the blood, heart, or bones. A subgroup of stem cells, the neural stem cells (NSCs), is characterized as a self-renewing population that generates neurons and glia of the developing brain. They can be isolated, genetically manipulated and differentiated in vitro and reintroduced into a developing, adult or a pathologically altered central nervous system. NSCs have been considered for use in cell replacement therapies in various neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. Characterization of genes with tightly controlled expression patterns during differentiation represents an approach to understanding the regulation of stem cell commitment. The regulation of stem cell biology by the ATP-binding cassette (ABC) transporters has emerged as an important new field of investigation. As a major focus of stem cell research is in the manipulation of cells to enable differentiation into a targeted cell population; in this review, we discuss recent literatures on ABC transporters and stem cells, and propose an integrated view on the role of the ABC transporters, especially ABCA2, ABCA3, ABCB1 and ABCG2, in NSCs' proliferation, differentiation and regulation, along with comparisons to that in hematopoietic and other stem cells.