Adult stem cells. (17/4797)

Development of a multicellular organism is accomplished through a series of events that are preprogrammed in the genome. These events encompass cellular proliferation, lineage commitment, lineage progression, lineage expression, cellular inhibition, and regulated apoptosis. The sequential progression of cells through these events results in the formation of the differentiated cells, tissues, and organs that constitute an individual. Although most cells progress through this sequence during development, a few cells leave the developmental continuum to become reserve precursor cells. The reserve precursor cells are involved in the continual maintenance and repair of the tissues and organs throughout the life span of the individual. Until recently it was generally assumed that the precursor cells in postnatal individuals were limited to lineage-committed progenitor cells specific for various tissues. However, studies by Young, his colleagues, and others have demonstrated the presence of two categories of precursor cells that reside within the organs and tissues of postnatal animals. These two categories of precursor cells are lineage-committed (multipotent, tripotent, bipotent, and unipotent) progenitor cells and lineage-uncommitted pluripotent (epiblastic-like, ectodermal, mesodermal, and endodermal) stem cells. These reserve precursor cells provide for the continual maintenance and repair of the organism after birth.  (+info)

Adult stem cells and their cardiac potential. (18/4797)

Adult cardiac muscle is unable to repair itself following severe disease or injury. Because of this fundamental property of the myocardium, it was long believed that the adult myocardium is a postmitotic tissue. Yet, recent studies have indicated that new cardiac myocytes are generated throughout the life span of an adult and that extracardiac cells can contribute to the renewal of individual cells within the myocardium. In addition, investigations of the phenotypic capacity of adult stem cells have suggested that their potential is not solely restricted to the differentiated cell phenotypes of the source tissue. These observations have great implications for cardiac biology, as stem cells obtained from the bone marrow and other readily accessible adult tissues may serve as a source of replacement cardiac myocytes. In this review, we describe the evidence for these new findings and discuss their implications in context of the continuing controversy over stem cell plasticity.  (+info)

Interleukin-6 deficiency affects bone marrow stromal precursors, resulting in defective hematopoietic support. (19/4797)

Interleukin-6 (IL-6) is a critical factor in the regulation of stromal function and hematopoiesis. In vivo bromodeoxyuridine incorporation analysis indicates that the percentage of Lin(-)Sca-1(+) hematopoietic progenitors undergoing DNA synthesis is diminished in IL-6-deficient (IL-6(-/-)) bone marrow (BM) compared with wild-type BM. Reduced proliferation of IL-6(-/-) BM progenitors is also observed in IL-6(-/-) long-term BM cultures, which show defective hematopoietic support as measured by production of total cells, granulocyte macrophage-colony-forming units (CFU-GMs), and erythroid burst-forming units (BFU-Es). Seeding experiments of wild-type and IL-6(-/-) BM cells on irradiated wild-type or IL-6-deficient stroma indicate that the hematopoietic defect can be attributed to the stromal and not to the hematopoietic component. In IL-6(-/-) BM, stromal mesenchymal precursors, fibroblast CFUs (CFU-Fs), and stroma-initiating cells (SICs) are reduced to almost 50% of the wild-type BM value. Moreover, IL-6(-/-) stromata show increased CD34 and CD49e expression and reduced expression of the membrane antigens vascular cell adhesion molecule-1 (VCAM-1), Sca-1, CD49f, and Thy1. These data strongly suggest that IL-6 is an in vivo growth factor for mesenchymal precursors, which are in part implicated in the reduced longevity of the long-term repopulating stem cell compartment of IL-6(-/-) mice.  (+info)

Homing of in vitro expanded Stro-1- or Stro-1+ human mesenchymal stem cells into the NOD/SCID mouse and their role in supporting human CD34 cell engraftment. (20/4797)

The Stro-1 antigen potentially defines a mesenchymal stem cell (MSC) progenitor subset. We here report on the role of human ex vivo-expanded selected Stro-1(+) or Stro-1(-) MSC subsets on the engraftment of human CD34(+) cord blood cells in the nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mouse model. The data show that cotransplantation of expanded Stro-1(-) cells with CD34(+) cells resulted in a significant increase of human CD45, CD34, CD19, and CD11b cells detected in blood or in bone marrow (BM) and spleen as compared with the infusion of CD34(+) cells alone. Infusion into mice of expanded Stro-1(+) and Stro-1(-) cells (without CD34(+) cells) showed that the numbers of Stro-1(+)-derived (as assessed by DNA analysis of human beta-globin with quantitative polymerase chain reaction [PCR]) were higher than Stro-1(-)-derived cells in spleen, muscles, BM, and kidneys, while more Stro-1(-)-derived than Stro-1(+)-derived cells were found in lungs. The transduction of expanded Stro-1(+) cells with an enhanced green fluorescent protein (eGFP) gene did not modify their cytokine release and their homing in NOD/SCID mouse tissues. The difference between the hematopoietic support and the homing capabilities of expanded Stro-1(+) and Stro-1(-) cells may be of importance for clinical therapeutic applications: Stro-1(+) cells may rather be used for gene delivery in tissues while Stro-1(-) cells may rather be used to support hematopoietic engraftment.  (+info)

Transduction of bone-marrow-derived mesenchymal stem cells by using lentivirus vectors pseudotyped with modified RD114 envelope glycoproteins. (21/4797)

Bone-marrow-derived mesenchymal stem cells (MSCs) have attracted considerable attention as tools for the systemic delivery of therapeutic proteins in vivo, and the ability to efficiently transfer genes of interest into such cells would create a number of therapeutic opportunities. We have designed and tested a series of human immunodeficiency virus type 1 (HIV-1)-based vectors and vectors based on the oncogenic murine stem cell virus to deliver and express transgenes in human MSCs. These vectors were pseudotyped with either the vesicular stomatitis virus G (VSV-G) glycoprotein (GP) or the feline endogenous virus RD114 envelope GP. Transduction efficiencies and transgene expression levels in MSCs were analyzed by quantitative flow cytometry and quantitative real-time PCR. While transduction efficiencies with virus particles pseudotyped with the VSV-G GP were found to be high, RD114 pseudotypes revealed transduction efficiencies that were 1 to 2 orders of magnitude below those observed with VSV-G pseudotypes. However, chimeric RD114 GPs, with the transmembrane and extracellular domains fused to the cytoplasmic domain derived from the amphotropic Moloney murine leukemia virus 4070A GP, revealed about 15-fold higher titers relative to the unmodified RD114 GP. The transduction efficiencies in human MSCs of HIV-1-based vectors pseudotyped with the chimeric RD114 GP were similar to those obtained with HIV-1 vectors pseudotyped with the VSV-G GP. Our results also indicate that RD114 pseudotypes were less toxic than VSV-G pseudotypes in human MSC progenitor assays. Taken together, these results suggest that lentivirus pseudotypes bearing alternative Env GPs provide efficient tools for ex vivo modification of human MSCs.  (+info)

Gene therapy approaches for bone regeneration. (22/4797)

Gene therapy represents a promising approach for delivering regenerative molecules to specific tissues including bone. Several laboratories have shown that virus-based BMP expression vectors can stimulate osteoblast differentiation and bone formation in vivo. Both in vivo and ex vivo transduction of cells can induce bone formation at ectopic and orthotopic sites. Adenovirus and direct DNA delivery of genes encoding regenerative molecules can heal critical-sized defects of cranial and long bones. Although osteogenic activity can be demonstrated for individual BMP vectors, substantial synergies may be achieved using combinatorial gene therapy to express complimentary osteogenic signals including specific combinations of BMPs or BMPs and transcription factors. Further control of the bone regeneration process may also be achieved through the use of inducible promoters that can be used to control the timing and magnitude of expression for a particular gene. Using these types of approaches, it should be possible to mimic natural processes of bone development and fracture repair and, in so doing, be able to precisely control both the amount and type of bone regenerated.  (+info)

p21Cip1 levels differentially regulate turnover of mature endothelial cells, endothelial progenitor cells, and in vivo neovascularization. (23/4797)

p21(Cip1) (p21) controls cell cycle progression and apoptosis in mature endothelial cells (ECs) and regulates size and cycling of the hematopoietic progenitor cell pool. Because circulating endothelial progenitor cells (EPCs) contribute to postnatal neovascularization in addition to mature ECs, we investigated the regulation of ECs and EPCs in p21-deficient mice. Mature aortic EC proliferation was increased in homozygous p21(-/-) and heterozygous p21(+/-) mice, in which p21 protein levels are reduced to one third of wild-type (WT). In contrast, apoptosis sensitivity was increased by 3.5-fold only in p21(-/-), but not in p21(+/-) mice. Consistently, in vivo apoptosis of ECs within areas of neovascularization was elevated in p21(-/-) but not in p21(+/-) mice. EPC numbers were elevated 2-fold in p21(-/-) mice compared with WT (P<0.001), and clonal expansion capacity of EPCs was increased from 25+/-4 (WT) to 57+/-8 colony-forming units in p21(-/-) mice (P<0.005). EPC numbers and expansion were likewise increased in p21(+/-) mice. As the integrative endpoint, in vivo neovascularization reflecting all p21-affected parameters was increased over WT only in p21(+/-) (P<0.001), but not in p21(-/-) mice. In conclusion, reduced p21 protein levels of mice lacking one p21 allele are associated with increased proliferation of ECs and EPCs, whereas survival of ECs to apoptotic stimuli in vitro and in vivo is not impaired. Under these conditions, neovascularization was increased. In contrast, complete p21 deficiency did not result in an increased neovascularization despite increased mature EC and EPC proliferation. This may be due to the sensitization of ECs against apoptosis.  (+info)

Effect of hydroxyurea and etoposide on transduction of human bone marrow mesenchymal stem and progenitor cell by adeno-associated virus vectors. (24/4797)

AIM: To study the effect of hydroxyurea and etoposide on transduction of human marrow mesenchymal and progenitor stem cells by adeno-associated virus (AAV). METHODS: Isolated human bone marrow mesenchymal stem and progenitor cells (hMSCs) were cultured in DMEM containing 10% FBS or 5% FBS and dexamethasone 1 micromol/L respectively. After being treated with hydroxyurea and etoposide, hMSCs were transduced by AAV-LUC. After two days luciferase activity (relative light unites per second or RLU/s) were tested, which indirectly reflected the relative transduction efficiency of different groups, and virus DNA was isolated by Hirt extraction for Southern hybridization. RESULTS: Transduction luciferase activity and transduction efficiency in cultures treated with hydroxyurea and etoposide were significantly higher than that in control cultures. Dividing cells had about 20-fold higher transduction efficiency compared with control cells. Transduction efficiency in stationary cells was about 50 times higher than that in control cells. Southern analysis showed that hydroxyurea and etoposide enhanced second-strand DNA synthesis by rAAV. CONCLUSION: Hydroxyurea and etoposide could increase transduction efficiency of hMSCs by AAV vectors, and stationary cells were more sensitive to these drugs than dividing cells.  (+info)