Several recent studies in animals as well as humans support the notion that bone marrow (BM)-derived cells participate in myocardial regeneration. However, this subject remains highly controversial and the identity of the specific cell type responsible for regeneration remains unknown. Recent work from our laboratory revealed that BM contains a highly mobile population of CXCR4+ cells that express mRNA for various markers of early tissue-committed stem cells (TCSC) and which are distinct from hematopoietic stem cells (HSC) (

Leukemia
2004
:
18
;
29
–40
). In the current study we investigated whether BM also contains a mobile pool of TCSC destined to differentiate into cardiomyocytes. Our data demonstrate that TCSC for cardiomyocytes (i) are present in significant amounts in BM harvested from young (1–2 month-old) while being barely detectable in older (1-year-old) mice; ii) reside in populations of murine BM-derived non-hematopoietic Sca-1+ CD45− cells and in population of human CXCR4+ CD34+ AC133+ CD45− BMMNC, iii) are mobilized from BM into peripheral blood (PB) during pharmacological mobilization or myocardial infarction; iv) the identified by us chemoattractants for these cells: stromal derived factor -1 (SDF-1), and hepatocyte growth factor/scatter factor (HGF/SF) are upregulated in infarcted myocardium, and v) blocking experiments with T140 (CXCR4 antagonist) and K252a (c-MET antagonist) confirmed that TCSC for cardiomyocytes are chemoattracted to the damaged myocardium in SDF-1-CXCR4 and SF/HGF-c-Met dependent manner. Thus, we conclude that the bone marrow is a potential source of TCSC for heart repair and since purified CD45+ HSC neither express cardiac markers nor differentiate in vitro into cardiomyocytes, we provide for the first time evidence that cardiac TCSC residing in bone marrow but not “plastic” HSC may account for cardiac differentiation of BM-derived cells. These observations provide rationale for further studies aimed at optimizing therapeutic cardiac regeneration by BM-derived non-hematopoietic cardiac TCSC. Finally, our observation that the number of marrow derived mobile/circulating cardiac TCSC is the highest in BM of young animals and decreases with age provides a novel insight into aging and may explain why the heart regeneration process becomes less effective in older individuals.

Topics:
bone marrow, cd45 antigens, cxcr4 receptors, myocardial infarction, myocardium, stem cells, antagonists, hepatocyte growth factor, cardiac markers, cd34 antigens

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2005, The American Society of Hematology
2004
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