Author
Stephen H. Bartelmez
Other affiliations: University of Florida
Bio: Stephen H. Bartelmez is an academic researcher from University of Washington. The author has contributed to research in topics: Progenitor cell & Stem cell. The author has an hindex of 11, co-authored 21 publications receiving 2900 citations. Previous affiliations of Stephen H. Bartelmez include University of Florida.
Papers
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TL;DR: Results indicate that haematopoietic stem cells do not readily acquire a cardiac phenotype, and raise a cautionary note for clinical studies of infarct repair.
Abstract: The mammalian heart has a very limited regenerative capacity and, hence, heals by scar formation. Recent reports suggest that haematopoietic stem cells can transdifferentiate into unexpected phenotypes such as skeletal muscle, hepatocytes, epithelial cells, neurons, endothelial cells and cardiomyocytes, in response to tissue injury or placement in a new environment. Furthermore, transplanted human hearts contain myocytes derived from extra-cardiac progenitor cells, which may have originated from bone marrow. Although most studies suggest that transdifferentiation is extremely rare under physiological conditions, extensive regeneration of myocardial infarcts was reported recently after direct stem cell injection, prompting several clinical trials. Here, we used both cardiomyocyte-restricted and ubiquitously expressed reporter transgenes to track the fate of haematopoietic stem cells after 145 transplants into normal and injured adult mouse hearts. No transdifferentiation into cardiomyocytes was detectable when using these genetic techniques to follow cell fate, and stem-cell-engrafted hearts showed no overt increase in cardiomyocytes compared to sham-engrafted hearts. These results indicate that haematopoietic stem cells do not readily acquire a cardiac phenotype, and raise a cautionary note for clinical studies of infarct repair.
2,239 citations
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TL;DR: It is shown that the continuous presence of TGF-beta 1 directly inhibits the cell division of essentially all low Ho/Rh cells during their 0 to 5th cell division in vitro, which must directly inhibit the proliferation of LTR-HSC contained within these low Ho-Rh cells.
201 citations
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TL;DR: The results demonstrate that TPO can mediate the self-replication of HSC in LTBMC, and provide proof that HSC can self-Replication ex vivo.
Abstract: The hematopoietic stem cell (HSC) is defined as a cell that can either self-replicate or generate daughter cells that are destined to commit to mature cells of different specific lineages. Self-replication of the most primitive HSC produces daughter cells that possess a long (possibly unlimited) clonal lifespan, whereas differentiation of HSC produces daughter cells that demonstrate a progressive reduction of their clonal lifespan, a loss of multilineage potential, and lineage commitment. Previous studies indicated that the proliferation of HSC ex vivo favors differentiation at the expense of self-replication, eventually resulting in a complete loss of HSC. In contrast, transplantation studies have shown that a single HSC can repopulate the marrow of a lethally irradiated mouse, demonstrating that self-renewal of HSC occurs in vivo. Thrombopoietin (TPO) has been shown to function both as a proliferative and differentiative factor for megakaryocytes and as a survival and weakly proliferative factor for HSC. Our studies focused on the effects of exogenous TPO on HSC in mouse long-term bone marrow cultures (LTBMC). Previous results indicate that HSC decline in LTBMC in the absence of TPO. In contrast, the continuous presence of TPO resulted in the generation of both long- and short-term repopulating HSC as detected by an in vivo competitive repopulation assay. HSC were generated over a 4-month period at concentrations similar to normal bone marrow. Our results demonstrate that TPO can mediate the self-replication of HSC in LTBMC, and provide proof that HSC can self-replicate ex vivo.
156 citations
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TL;DR: MIP-1 alpha and TGF beta are direct bidirectional regulators of HPC growth, whose effects are dependent on other growth factors present as well as the maturational state of the HPC assayed.
88 citations
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TL;DR: The BM microenvironment of type 1 diabetic mice can lead to changes in haematopoiesis, with generation of more monocytes and fewer EPCs contributing to development of microvascular complications and inhibition of GP130 activation may serve as a therapeutic strategy to improve the key aspects of this dysfunction.
Abstract: Aims/hypothesis
We sought to determine the impact of long-standing type 1 diabetes on haematopoietic stem/progenitor cell (HSC) number and function and to examine the impact of modulating glycoprotein (GP)130 receptor in these cells.
86 citations
Cited by
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TL;DR: Naive mesenchymal stem cells are shown here to specify lineage and commit to phenotypes with extreme sensitivity to tissue-level elasticity, consistent with the elasticity-insensitive commitment of differentiated cell types.
12,204 citations
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TL;DR: Several studies which tested the use of MSCs in models of infarct (injured heart), stroke (brain), or meniscus regeneration models are reviewed within the context of M SC‐mediated trophic effects in tissue repair.
Abstract: Adult marrow-derived Mesenchymal Stem Cells (MSCs) are capable of dividing and their progeny are further capable of differentiating into one of several mesenchymal phenotypes such as osteoblasts, chondrocytes, myocytes, marrow stromal cells, tendon-ligament fibroblasts, and adipocytes. In addition, these MSCs secrete a variety of cytokines and growth factors that have both paracrine and autocrine activities. These secreted bioactive factors suppress the local immune system, inhibit fibrosis (scar formation) and apoptosis, enhance angiogenesis, and stimulate mitosis and differentiation of tissue-intrinsic reparative or stem cells. These effects, which are referred to as trophic effects, are distinct from the direct differentiation of MSCs into repair tissue. Several studies which tested the use of MSCs in models of infarct (injured heart), stroke (brain), or meniscus regeneration models are reviewed within the context of MSC-mediated trophic effects in tissue repair.
2,743 citations
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TL;DR: Intracoronary transfer of autologous bone-marrow-cells promotes improvement of left-ventricular systolic function in patients after acute myocardial infarction.
2,233 citations
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TL;DR: This work generated highly purified human cardiomyocytes using a readily scalable system for directed differentiation that relies on activin A and BMP4, and identified a cocktail of pro-survival factors that limitsCardiomyocyte death after transplantation.
Abstract: Cardiomyocytes derived from human embryonic stem (hES) cells potentially offer large numbers of cells to facilitate repair of the infarcted heart. However, this approach has been limited by inefficient differentiation of hES cells into cardiomyocytes, insufficient purity of cardiomyocyte preparations and poor survival of hES cell-derived myocytes after transplantation. Seeking to overcome these challenges, we generated highly purified human cardiomyocytes using a readily scalable system for directed differentiation that relies on activin A and BMP4. We then identified a cocktail of pro-survival factors that limits cardiomyocyte death after transplantation. These techniques enabled consistent formation of myocardial grafts in the infarcted rat heart. The engrafted human myocardium attenuated ventricular dilation and preserved regional and global contractile function after myocardial infarction compared with controls receiving noncardiac hES cell derivatives or vehicle. The ability of hES cell-derived cardiomyocytes to partially remuscularize myocardial infarcts and attenuate heart failure encourages their study under conditions that closely match human disease.
2,173 citations
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TL;DR: The potential paracrine mechanisms involved in adult stem cell signaling and therapy are reviewed: cytokines and growth factors can induce cytoprotection and neovascularization, and cardiac remodeling, contractility, and metabolism may also be influenced in aParacrine fashion.
Abstract: Animal and preliminary human studies of adult cell therapy following acute myocardial infarction have shown an overall improvement of cardiac function. Myocardial and vascular regeneration have been initially proposed as mechanisms of stem cell action. However, in many cases, the frequency of stem cell engraftment and the number of newly generated cardiomyocytes and vascular cells, either by transdifferentiation or cell fusion, appear too low to explain the significant cardiac improvement described. Accordingly, we and others have advanced an alternative hypothesis: the transplanted stem cells release soluble factors that, acting in a paracrine fashion, contribute to cardiac repair and regeneration. Indeed, cytokines and growth factors can induce cytoprotection and neovascularization. It has also been postulated that paracrine factors may mediate endogenous regeneration via activation of resident cardiac stem cells. Furthermore, cardiac remodeling, contractility, and metabolism may also be influenced in a paracrine fashion. This article reviews the potential paracrine mechanisms involved in adult stem cell signaling and therapy.
1,855 citations