Abstract—The accepted paradigm considers the adult mammalian heart as a postmitotic organ, which ... more Abstract—The accepted paradigm considers the adult mammalian heart as a postmitotic organ, which possesses a relatively constant number,of myocytes,from shortly after birth to adulthood and senescence. This notion is questioned by the demonstration that although most adult myocytes are terminally differentiated, there is a small and continuously renewed,subpopulation of cycling myocytes,produced by the differentiation of cardiac stem-like cells. Myocyte death
Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects o... more Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects of myocardial ischemia. On this basis, CAN was produced in female FVB.Igf1/- mice and nontransgenic littermates, and the animals were euthanized 7 days later. CAN consisted of an 82% reduction in the vessel luminal cross-sectional area in both groups of mice. Severe left ventricular dysfunction was present in
A major debate of the last decade involves the plasticity of c-kit-positive bone marrow cells (c-... more A major debate of the last decade involves the plasticity of c-kit-positive bone marrow cells (c-kit-BMCs) and their ability to acquire cell lineages different from the organ of origin. Conflicting results obtained in different laboratories may depend on the functional heterogeneity and distinct transdifferentiation potential of single c-kit-BMCs. To address this issue, two methodologies were employed to label individual c-kit-BMCs and define their clonal fate in vivo: viral gene-tagging and fluorescent protein-based multicolor cell marking. c-kit-BMCs were infected with EGFP lentiviruses and injected in infarcted hearts. At 2 weeks, the regenerated myocardium was enzymatically digested and EGFP-labeled myocytes, endothelial cells, fibroblasts, and c-kit-cells were sorted. By employing a PCR-based method of detection of viral integrants, we searched for unique sites of viral insertion in the infected c-kit-BMCs and their progeny. Common insertion sites were found in the DNA of c-kit...
The critical role that stem cell niches have in cardiac homeostasis and myocardial repair followi... more The critical role that stem cell niches have in cardiac homeostasis and myocardial repair following injury is the focus of this review. Cardiac niches represent specialized microdomains where the quiescent and activated state of resident stem cells is regulated. Alterations in niche function with aging and cardiac diseases result in abnormal sites of cardiomyogenesis and inadequate myocyte formation. The relevance of Notch1 signaling, gap-junction formation, HIF-1α and metabolic state in the regulation of stem cell growth and differentiation within the cardiac niches are discussed.
To test the hypothesis that early interventional treatment with insulin-like growth factor-1 (IGF... more To test the hypothesis that early interventional treatment with insulin-like growth factor-1 (IGF-1) alleviates subsequent development of dilated cardiomyopathy, cardiac-specific IGF-1 expression was introduced by selective cross-breeding into a transgenic mouse model of heart failure that displays phenotypic characteristics of severe dilation. Hemodynamic, structural, and cellular parameters of the heart were compared between nontransgenic, tropomodulin-overexpressing cardiomyopathic, and the hybrid tropomodulin/IGF-1-overexpressing mice. Beneficial effects of IGF-1 were apparent by multiple indices of cardiac structure and function, including normalization of heart mass, anatomy, hemodynamics, and apoptosis. IGF-1 expression also acted as a proliferative stimulus as evidenced by calculated increases in myocyte number as well as expression of Ki67, a nuclear marker of cellular replication. Cellular analyses revealed that IGF-1 inhibited characteristic cardiomyocyte elongation in di...
STEM CELLS® is a monthly publication, it has been published continuously since 1983. The genetics... more STEM CELLS® is a monthly publication, it has been published continuously since 1983. The genetics and genomics; translational and clinical research; technology development. embryonic stem cells; tissue-specific stem cells; cancer stem cells; the stem cell niche; stem cell STEM CELLS®, an international peer-reviewed journal, covers all aspects of stem cell research: by ABSTRACT This review discusses the current controversy about the role that endogenous and exogenous progenitor cells have in cardiac homeostasis and myocardial regeneration following injury. Although great enthusiasm was created by the possibility of reconstituting the damaged heart, the opponents of this new concept of cardiac biology have interpreted most of the findings supporting this possibil-ity as the product of technical artifacts. This article challenges this established, static view of cardiac growth and favors the notion that the mammalian heart has the inherent ability to replace its cardiomyocytes through the activation of a pool of resident primitive cells or the administration of hematopoietic stem cells. STEM CELLS 2007;25:589 -601
To determine whether adult cardiac myocytes are capable of multiple divisions and whether this fo... more To determine whether adult cardiac myocytes are capable of multiple divisions and whether this form of growth is restricted to a subpopulation of cells that retain this capacity with age, telomere lengths were measured in myocyte nuclei isolated from the left ventricle of fetal and neonatal Fischer 344 rats and rats at 4, 12, and 27 months after birth. Two independent methodologies were used for this analysis: laser scanning cytometer and confocal microscopy. In each case, fluorescence intensity of a peptide nucleic acid probe specific for telomeric sequence was evaluated. The two techniques yielded comparable results. Telomeric shortening increased with age in a subgroup of myocytes that constituted 16% of the entire cell population. In the remaining nondividing cells, progressive accumulation of a senescent associated nuclear protein, p16 INK4 , was evidenced. In conclusion, a significant fraction of myocytes divides repeatedly from birth to senescence, counteracting the continuous death of cells in the aging mammalian rat heart. (Am J Pathol 2000, 156:813-819)
ABSTRACT Chromosome replication and oxidative DNA damage lead to shortening of telomeres, promoti... more ABSTRACT Chromosome replication and oxidative DNA damage lead to shortening of telomeres, promoting signaling pathways culminating in replicative senescence and cell cycle arrest. But whether inherited short telomeres impact on the electromechanical properties of adult cardiomyocyte, ultimately affecting ventricular performance, remains to be clarified. For this purpose, homozygous telomerase RNA component (Terc) deficient mice (KO) were employed, because they present defective telomerase, an enzyme involved in preserving telomere integrity in dividing cells. Third generation Terc-KO mice, which exhibit critical telomere shortening, were studied and compared to age-and sex-matched WT. At 3-4 months, Terc-KO mice showed slightly depressed LV function assessed by invasive hemodynamics, in respect to WT. At ~12 months, systolic and diastolic indices of LV performance were deteriorated in KO with respect to WT, together with protraction of the electrical recovery, assessed by ECG. To establish whether defective myocyte properties contributed to the impaired cardiac function, LV isolated cell preparations from WT and KO mice at 12 months, were studied. WT and Terc-KO mice had comparable cell size, excluding the occurrence of hypertrophic remodeling. By patch-clamp, under intracellular Ca2+ buffered condition, action potential amplitude and duration were comparable in the two groups of cells. Additionally, L-type Ca2+ current, responsible for triggering cell contraction, was not affected by the shortened telomeres. In contrast, using Fluo-4 loaded cells in field stimulation, Ca2+ transient decay in Terc-KO myocytes was significantly prolonged (+20%) with respect to WT, suggesting defective clearance of this cation from the cytoplasm, which represents a typical feature of the senescent myocardium. Importantly, myocyte relaxation was slower in KO, together with weaker cell contraction. Differences in mechanical function between the two cell types were abolished following isoproterenol exposure, indicating that contractile reserve was not impaired in Terc mice. In conclusion, myocytes with shortened telomeres present abnormalities in Ca2+ cycling and mechanical function which negatively impact on cardiac performance.
Abstract—The accepted paradigm considers the adult mammalian heart as a postmitotic organ, which ... more Abstract—The accepted paradigm considers the adult mammalian heart as a postmitotic organ, which possesses a relatively constant number,of myocytes,from shortly after birth to adulthood and senescence. This notion is questioned by the demonstration that although most adult myocytes are terminally differentiated, there is a small and continuously renewed,subpopulation of cycling myocytes,produced by the differentiation of cardiac stem-like cells. Myocyte death
Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects o... more Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects of myocardial ischemia. On this basis, CAN was produced in female FVB.Igf1/- mice and nontransgenic littermates, and the animals were euthanized 7 days later. CAN consisted of an 82% reduction in the vessel luminal cross-sectional area in both groups of mice. Severe left ventricular dysfunction was present in
A major debate of the last decade involves the plasticity of c-kit-positive bone marrow cells (c-... more A major debate of the last decade involves the plasticity of c-kit-positive bone marrow cells (c-kit-BMCs) and their ability to acquire cell lineages different from the organ of origin. Conflicting results obtained in different laboratories may depend on the functional heterogeneity and distinct transdifferentiation potential of single c-kit-BMCs. To address this issue, two methodologies were employed to label individual c-kit-BMCs and define their clonal fate in vivo: viral gene-tagging and fluorescent protein-based multicolor cell marking. c-kit-BMCs were infected with EGFP lentiviruses and injected in infarcted hearts. At 2 weeks, the regenerated myocardium was enzymatically digested and EGFP-labeled myocytes, endothelial cells, fibroblasts, and c-kit-cells were sorted. By employing a PCR-based method of detection of viral integrants, we searched for unique sites of viral insertion in the infected c-kit-BMCs and their progeny. Common insertion sites were found in the DNA of c-kit...
The critical role that stem cell niches have in cardiac homeostasis and myocardial repair followi... more The critical role that stem cell niches have in cardiac homeostasis and myocardial repair following injury is the focus of this review. Cardiac niches represent specialized microdomains where the quiescent and activated state of resident stem cells is regulated. Alterations in niche function with aging and cardiac diseases result in abnormal sites of cardiomyogenesis and inadequate myocyte formation. The relevance of Notch1 signaling, gap-junction formation, HIF-1α and metabolic state in the regulation of stem cell growth and differentiation within the cardiac niches are discussed.
To test the hypothesis that early interventional treatment with insulin-like growth factor-1 (IGF... more To test the hypothesis that early interventional treatment with insulin-like growth factor-1 (IGF-1) alleviates subsequent development of dilated cardiomyopathy, cardiac-specific IGF-1 expression was introduced by selective cross-breeding into a transgenic mouse model of heart failure that displays phenotypic characteristics of severe dilation. Hemodynamic, structural, and cellular parameters of the heart were compared between nontransgenic, tropomodulin-overexpressing cardiomyopathic, and the hybrid tropomodulin/IGF-1-overexpressing mice. Beneficial effects of IGF-1 were apparent by multiple indices of cardiac structure and function, including normalization of heart mass, anatomy, hemodynamics, and apoptosis. IGF-1 expression also acted as a proliferative stimulus as evidenced by calculated increases in myocyte number as well as expression of Ki67, a nuclear marker of cellular replication. Cellular analyses revealed that IGF-1 inhibited characteristic cardiomyocyte elongation in di...
STEM CELLS® is a monthly publication, it has been published continuously since 1983. The genetics... more STEM CELLS® is a monthly publication, it has been published continuously since 1983. The genetics and genomics; translational and clinical research; technology development. embryonic stem cells; tissue-specific stem cells; cancer stem cells; the stem cell niche; stem cell STEM CELLS®, an international peer-reviewed journal, covers all aspects of stem cell research: by ABSTRACT This review discusses the current controversy about the role that endogenous and exogenous progenitor cells have in cardiac homeostasis and myocardial regeneration following injury. Although great enthusiasm was created by the possibility of reconstituting the damaged heart, the opponents of this new concept of cardiac biology have interpreted most of the findings supporting this possibil-ity as the product of technical artifacts. This article challenges this established, static view of cardiac growth and favors the notion that the mammalian heart has the inherent ability to replace its cardiomyocytes through the activation of a pool of resident primitive cells or the administration of hematopoietic stem cells. STEM CELLS 2007;25:589 -601
To determine whether adult cardiac myocytes are capable of multiple divisions and whether this fo... more To determine whether adult cardiac myocytes are capable of multiple divisions and whether this form of growth is restricted to a subpopulation of cells that retain this capacity with age, telomere lengths were measured in myocyte nuclei isolated from the left ventricle of fetal and neonatal Fischer 344 rats and rats at 4, 12, and 27 months after birth. Two independent methodologies were used for this analysis: laser scanning cytometer and confocal microscopy. In each case, fluorescence intensity of a peptide nucleic acid probe specific for telomeric sequence was evaluated. The two techniques yielded comparable results. Telomeric shortening increased with age in a subgroup of myocytes that constituted 16% of the entire cell population. In the remaining nondividing cells, progressive accumulation of a senescent associated nuclear protein, p16 INK4 , was evidenced. In conclusion, a significant fraction of myocytes divides repeatedly from birth to senescence, counteracting the continuous death of cells in the aging mammalian rat heart. (Am J Pathol 2000, 156:813-819)
ABSTRACT Chromosome replication and oxidative DNA damage lead to shortening of telomeres, promoti... more ABSTRACT Chromosome replication and oxidative DNA damage lead to shortening of telomeres, promoting signaling pathways culminating in replicative senescence and cell cycle arrest. But whether inherited short telomeres impact on the electromechanical properties of adult cardiomyocyte, ultimately affecting ventricular performance, remains to be clarified. For this purpose, homozygous telomerase RNA component (Terc) deficient mice (KO) were employed, because they present defective telomerase, an enzyme involved in preserving telomere integrity in dividing cells. Third generation Terc-KO mice, which exhibit critical telomere shortening, were studied and compared to age-and sex-matched WT. At 3-4 months, Terc-KO mice showed slightly depressed LV function assessed by invasive hemodynamics, in respect to WT. At ~12 months, systolic and diastolic indices of LV performance were deteriorated in KO with respect to WT, together with protraction of the electrical recovery, assessed by ECG. To establish whether defective myocyte properties contributed to the impaired cardiac function, LV isolated cell preparations from WT and KO mice at 12 months, were studied. WT and Terc-KO mice had comparable cell size, excluding the occurrence of hypertrophic remodeling. By patch-clamp, under intracellular Ca2+ buffered condition, action potential amplitude and duration were comparable in the two groups of cells. Additionally, L-type Ca2+ current, responsible for triggering cell contraction, was not affected by the shortened telomeres. In contrast, using Fluo-4 loaded cells in field stimulation, Ca2+ transient decay in Terc-KO myocytes was significantly prolonged (+20%) with respect to WT, suggesting defective clearance of this cation from the cytoplasm, which represents a typical feature of the senescent myocardium. Importantly, myocyte relaxation was slower in KO, together with weaker cell contraction. Differences in mechanical function between the two cell types were abolished following isoproterenol exposure, indicating that contractile reserve was not impaired in Terc mice. In conclusion, myocytes with shortened telomeres present abnormalities in Ca2+ cycling and mechanical function which negatively impact on cardiac performance.
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