Biomedical subjects

Ross Summer

Publications and source records attributed to Ross Summer.

9 recordsLinked to original sources

PubMed2005

Restoration of cardiac progenitor cells after myocardial infarction by self-proliferation and selective homing of bone marrow-derived stem cells.

Tissue-specific progenitor cells contribute to local cellular regeneration and maintain organ function. Recently, we have determined that cardiac side-population (CSP) cells represent a distinct cardiac progenitor cell population, capable of in vitro differentiation into functional cardiomyocytes. The response of endogenous CSP to myocardial injury, however, and the cellular mechanisms that maintain this cardiac progenitor cell pool in vivo remain unknown. In this report we demonstrate that local progenitor cell proliferation maintains CSP under physiologic conditions, with little contribution from extracardiac stem cell sources. Following myocardial infarction in adult mice, however, CSP cells are acutely depleted, both within the infarct and noninfarct areas. CSP pools are subsequently reconstituted to baseline levels within 7 days after myocardial infarction, through both proliferation of resident CSP cells, as well as through homing of bone marrow-derived stem cells (BMC) to specific areas of myocardial injury and immunophenotypic conversion of BMC to adopt a CSP phenotype. We, therefore, conclude that following myocardial injury, cardiac progenitor cell populations are acutely depleted and are reconstituted to normal levels by both self-proliferation and selective homing of BMC. Understanding and enhancing such processes hold enormous potential for therapeutic myocardial regeneration.

Animals↗

PubMed2005

Gene expression profiling and localization of Hoechst-effluxing CD45- and CD45+ cells in the embryonic mouse lung.

Hoechst-effluxing cells (side population cells) are a rare subset of cells found in adult tissues that are highly enriched for stem and progenitor cell activity. To identify potential stem and progenitor cells during lung development, we generated gene expression profiles for CD45- and CD45+ side population cells in the embryonic day 17.5 lung. We found that side population cells comprise 1% of total embryonic day 17.5 lung cells (55% CD45+, 45% CD45-). Gene profiling data demonstrated an overrepresentation of endothelial genes within the CD45- side population. We used expression of several distinct genes to identify two types of CD45- side population cells: 1) von Willebrand factor+/smooth muscle actin+ cells that reside in the muscular layer of select large vessels and 2) von Willebrand factor+/intercellular adhesion molecule+ cells that reside within the endothelial layer of select small vessels. Gene profiling of the CD45+ side population indicated an overrepresentation of genes associated with myeloid cell differentiation. Consistent with this, culturing CD45+ side population cells was associated with induction of mature dendritic markers (CD86). The microarray results suggested that expression of myeloperoxidase and proteinase-3 might be used to identify CD45+ side population cells. By immunohistochemistry, we found that myeloperoxidase+/proteinase-3+ cells represent a small subset of total CD45+ cells in the embryonic day 17.5 lung and that they reside in the mesenchyme and perivascular regions. This is the first detailed information regarding the phenotype and localization of side population cells in a developing organ.

Animals↗

PubMed2005

Evidence that bone marrow cells do not contribute to the alveolar epithelium.

An ongoing controversy is the role of marrow cells in populating the alveolar epithelium. In this study, we employed flow cytometry and histologic techniques to evaluate this process. Donor bone marrow was harvested from transgenic mice expressing the LacZ or eGFP gene ubiquitously, or under the control of the human surfactant protein (SP)-C promoter, and transplanted into lethally irradiated, neonatal mice. In recipients transplanted with marrow that express eGFP or lacZ ubiquitously, light microscopy revealed cells whose morphology and location were compatible with a type II cell phenotype. Consistent with this, fluorescent microscopy suggested colocalization of eGFP and pro-SP-C proteins in single cells. In mice transplanted with SP-C-eGFP marrow, engraftment was not detectable by histology or flow cytometry. We therefore used deconvolution microscopy to reanalyze histologic sections that were thought to show marrow-derived type II cells. We found that all putative marrow-derived pneumocytes resulted from the overlapping fluorescent signals of an endogenous pro-SP-C+ type II cell and a donor-derived eGFP+ cell. Taken together, our observations underscore the technical difficulties associated with evaluating engraftment in lung, and argue against a contributory role for marrow cells in populating the alveolar epithelium.

Animals↗

PubMed2005

CD31- but Not CD31+ cardiac side population cells exhibit functional cardiomyogenic differentiation.

Heart failure remains a leading cause of morbidity and mortality. The cellular mechanism underlying the development of cardiac dysfunction is a decrease in the number of viable cardiomyocytes. Recent observations have suggested that the adult heart may contain a progenitor cell population. Side population (SP) cells, characterized by a distinct Hoechst dye efflux pattern, have been shown to exist in multiple tissues and are capable of tissue-specific differentiation. In this report, we confirm the existence of a cardiac SP cell population, immunophenotypically distinct from bone marrow SP cells. Moreover, we demonstrate that among cardiac SP cells, the greatest potential for cardiomyogenic differentiation is restricted to cells negative for CD31 expression and positive for stem cell antigen 1 (Sca1) expression (CD31-/Sca1+). Furthermore, we determine that CD31-/Sca1+ cardiac SP cells are capable of both biochemical and functional cardiomyogenic differentiation into mature cardiomyocytes, with expression of cardiomyocyte-specific transcription factors and contractile proteins, as well as stimulated cellular contraction and intracellular calcium transients indistinguishable from adult cardiomyocytes. We also determine the necessity of cell-extrinsic signaling through coupling, although not fusion, with adult cardiomyocytes in regulating cardiomyogenic differentiation of cardiac SP cells. We, therefore, conclude that CD31-/Sca1+ cardiac SP cells represent a distinct cardiac progenitor cell population, capable of cardiomyogenic differentiation into mature cardiomyocytes through a process mediated by cellular coupling with adult cardiomyocytes.

Animals↗

PubMed2005

Embryonic lung side population cells are hematopoietic and vascular precursors.

Side population (SP) cells are a select cell population identified by a capacity to efflux Hoechst dye that are highly enriched for stem/progenitor cell activity. In this study, we found that SP cells comprised of CD45(+) and CD45(-) subtypes are present in the embryonic lung (E-SP) at levels varying with gestational age. Long-term in vivo competitive blood reconstitution studies demonstrated that hematopoeitic stem cell capacity resided within the CD45(+) E-SP cell subset. Immunophenotyping of CD45(-) E-SP cells determined that this population consists of two subtypes: CD31(-) and CD31(+). Limited gene expression profiling indicated that CD45(-)/CD31(-) E-SP cells have features of smooth muscle precursors, and give rise to smooth muscle in culture. On the other hand, CD45(-)/CD31(+) E-SP cells express genes characteristic of endothelium, but by themselves do not grow or differentiate in culture. Co-culture of CD45(-)/CD31(+) and CD45(-)/CD31(-) E-SP cells, however, resulted in the formation of complex tubular networks that express markers of endothelium. Together, these findings illustrate that embryonic lung SP cells are heterogeneous, composed of hematopoeitic and nonhematopoeitic progenitors, and may play a key role in the formation of the lung vasculature.

Animals↗

PubMed2004

Translational physiology: origin and phenotype of lung side population cells.

Side population (SP) cells, a rare cell type identified by their ability to efflux the vital dye Hoechst 33342, are highly enriched for stem cell activity. Bone marrow (BM) SP cells uniformly express the pan-hematopoietic marker CD45, whereas tissue SP cells are heterogeneous in CD45 expression. In previous studies, we found that CD45 is expressed on 75% of lung SP cells. By performing whole BM transplantations, we determined that CD45-positive and CD45-negative lung SP cells are marrow derived. Transplantation of 200 highly purified BM SP cells indicated that both lung SP cell subtypes are derived from this marrow cell type. Morphologically, CD45-positive lung and BM SP cells possess similar features. They are small, round, and contain scant cytoplasm. CD45-negative lung SP cells are larger and contain abundant granular cytoplasm. Gene expression patterns for hematopoietic transcription factors GATA-1, GATA-2, and PU.1 further differentiated SP marrow and lung subtypes. By immunostaining for alpha-smooth muscle actin and cytokeratin, we found significant differences in the relative expression patterns of these markers in lung and marrow SP cell subtypes. In summary, these findings demonstrate that lung SP cells are derived from the BM and that CD45-positive and -negative subtypes can be distinguished by morphological differences and gene expression patterns.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2004

Lung stem cells: new paradigms.

The intrinsic anatomical complexity of the lung, its slow cell turnover, and the lack of regenerative models are among the factors that have complicated the study and isolation of adult lung stem cells. Despite this, several endogenous lung progenitor cells have been identified in the proximal and distal lung. However, there is limited data regarding the lineage relationships, self-renewal properties, and clonality of these specific lung cell progenitors. More recent work showing that marrow cells can engraft as differentiated cells of solid organs has suggested new stem cell paradigms for the lung. In this review, we explore the implications of these new studies for lung stem cell biology. We also summarize and discuss the ongoing controversies that these studies have generated.

Animals↗

PubMed2003

Akt signaling regulates side population cell phenotype via Bcrp1 translocation.

Akt is an important regulator of cell survival, growth, and glucose metabolism in many cell types, but the role of this signaling molecule in hematopoietic stem cells is poorly defined. Side population (SP) cells are enriched for hematopoietic stem cell activity and are defined by their ability to efficiently efflux Hoechst 33342. Bone marrow from Akt1-null mice exhibited a reduced SP fraction. However, bone marrow cellularity, growth factor-responsive progenitor cultures, and engraftable stem cells were normal in these mice. Treatment of bone marrow with LY294002, an inhibitor of the Akt effector protein phosphatidylinositol 3-kinase, led to a reversible loss of the SP fraction. Bcrp1, which encodes the Hoechst dye transporter, was translocated from the membrane to the intracellular compartment under conditions that promote the SP-depleted state. Lentivirus-mediated overexpression of Akt1 in bone marrow markedly increased the SP fraction, whereas there was no effect on bone marrow from Bcrp(-/-) mice. These data suggest that Akt signaling modulates the SP cell phenotype by regulating the expression of Bcrp1.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2003

Side population cells and Bcrp1 expression in lung.

Side population (SP) cells are a rare subset of cells found in various tissues that are highly enriched for stem cell activity. SP cells can be isolated by dual-wavelength flow cytometry because of their capacity to efflux Hoechst dye, a process mediated by the ATP-binding cassette transporter breast cancer resistance protein (Bcrp) 1. By performing flow cytometry of enzymedigested mouse lung stained with Hoechst dye, we found that SP cells comprise 0.03-0.07% of total lung cells and are evenly distributed in proximal and distal lung regions. By RT-PCR, we found that lung SP cells express hepatocyte nuclear factor-3beta, but not thyroid transcription factor-1. Surface marker analysis revealed lung SP cells to be stem cell antigen 1 positive, Bcrp1 positive, lineage marker negative, and heterogeneous at the CD45 locus. As expected, we did not detect lung SP cells in Bcrp1-deficient animals. We, therefore, employed nonisotopic in situ hybridization and immunostaining for Bcrp1 as a strategy to localize these cells in vivo. Expression was observed in distinct lung cell types: bronchial and vascular smooth muscle cells and round cells within the distal air space. We confirmed the expression of Bcrp1 in primary bronchial smooth muscle cell cultures (BSMC) and in lavaged distal airway cells, but neither possessed the capacity to efflux Hoechst dye. In BSMC, Bcrp1 was localized to an intracellular compartment, suggesting that the molecular site of Bcrp1 expression regulates SP phenotype.

ATP Binding Cassette Transporter, Subfamily G, Mem↗