doi: 10.1161/CIRCULATIONAHA.105.595181
(Circulation. 2006;113:1451-1463.)
© 2006 American Heart Association, Inc.
Basic Science for Clinicians |
Life and Death of Cardiac Stem Cells
A Paradigm Shift in Cardiac Biology
From the Cardiovascular Research Institute, Department of Medicine, New York Medical College, Valhalla, (P.A., J.K., A.L.); and the Institute of Molecular Cardiology, University of Louisville, Louisville, Ky (R.B.).
Correspondence to Piero Anversa, MD, Cardiovascular Research Institute, Vosburgh Pavilion, New York Medical College, Valhalla, NY 10595. E-mail piero_anversa{at}nymc.edu
Key Words: regeneration • heart failure • stem cells
 |
Introduction |
|---|
 Top Introduction The Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
The recognition that myocyte mitosis occurs in the fetal, neonatal, adult, and hypertrophied heart and that a pool of primitive, undifferentiated cells is present in the myocardium has put forward a different view of the biology of the heart. The new paradigm suggests that myocyte formation is preserved during postnatal life, in adulthood or senescence, pointing to a remarkable growth reserve of the heart throughout the course of life of the organism. This article reviews a large body of novel information, which has been obtained in the last 2 decades, in favor of the notion that the mammalian heart has the inherent ability to continuously replace its parenchymal cells and that this unexpected characteristic has important implications in understanding myocardial homeostasis, cardiac aging, and tissue repair.
|
The Heart Is a Self-Renewing Organ |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
The paradigm that the heart is a postmitotic organ incapable of regenerating parenchymal cells was established in the 1970s, and this dogma has profoundly conditioned basic and clinical research in cardiology for the last 3 decades. On the basis of this paradigm, cardiomyocytes undergo cellular hypertrophy1,2 but cannot be replaced either by entry into the cell cycle of a subpopulation of nonterminally differentiated myocytes or by activation of a pool of primitive cells that become committed to the myocyte lineage. The only response of cardiomyocytes to stress is hypertrophy and/or death. Therefore, a tremendous effort was made to identify the molecular mechanisms of myocyte hypertrophy and their genetic control. A sophisticated knowledge of various signaling pathways has been achieved, and our understanding of the biology of hypertrophic myocyte growth has advanced markedly.3 An array of new technologies has been introduced that has led to a scientific revolution in terms of questions, approaches, and interpretation of experimental results. Despite this enormous progress in our understanding of basic mechanisms of hypertrophy, however, very little has been translated into clinical interventions that interfere with the dramatic impact of ischemic myocardial injury and the devastating evolution of postinfarction heart failure.4
Recently, an established notion of cardiac biology has been questioned. The general belief that during prenatal life cardiac progenitor cells undergo progressive lineage commitment and differentiation,5 which results in an irreversible loss of developmental options in adulthood, may not be valid.6 Similarly, the traditional view of the heart as an organ incapable of regeneration has been challenged. Myocyte replication, karyokinesis, cytokinesis, and foci of spontaneous myocardial regeneration have been documented in the human heart.7,8 These observations, together with the recognition that cell division, telomerase activity, telomeric shortening, and apoptosis occur in myocytes with aging and cardiac failure,7,9,10 suggest that in the adult heart, a class of parenchymal cells proliferates, undergoes telomere attrition, reaches terminal differentiation, and possibly experiences replicative senescence and ultimately, cell death.
If adult, fully differentiated myocytes (
25 000 µm3 in volume) were to retain the ability to divide, cells in mitosis before cytokinesis would be expected to be 50 000 µm3 to give rise to 2 daughter cells, each 25 000 µm3. Surprisingly, human myocytes in mitosis vary in size from <1000 µm3 to at most 5000 µm3, indicating that a different mechanism of myocyte formation is operative in the adult heart.8,10–12 The replicating cardiomyocytes resemble small amplifying cells that have originated by activation of progenitor cells. These observations, together with the demonstration of male cells in female hearts transplanted in male recipients,13 were the critical findings that led to the identification and characterization of stem cells in the adult myocardium. The presence of male cells in the female heart raised the possibility that these cells either were the progeny of primitive cells of the recipient’s bone marrow, which homed to the heart through the systemic circulation, or represented the product of stemlike cells that had migrated to the allograft from cardiac remnants.14 The discovery of cardiac stem cells (CSCs)6,15–20 distinct from hematopoietic stem cells (HSCs) and minimal spontaneous engraftment of HSCs into the heart argue against a significant role of the bone marrow in the turnover of cardiac cells.21,22
The recognition that a pool of primitive cells resides in the myocardium and that these cells form myocytes, smooth muscle cells (SMCs), and endothelial cells (ECs)8,15,16,23 has provided a different perspective concerning the biology of the heart and mechanisms of myocardial homeostasis and tissue repair. The new paradigm implies that myocytes are no longer considered unusual cells that are created only during embryonic and fetal development so that their total number in the heart is established at birth and no further growth occurs postnatally, in adulthood, or during senescence.2,24 This paradigm refutes the belief that all cardiomyocytes have the same age and that the age of these cells corresponds to the age of the organ and organism. Similarly, this paradigm suggests that the turnover and growth of vascular SMCs and ECs may be regulated by differentiation of CSCs more than by the ability of these mature cells to reenter the cell cycle and divide.
Thus, a new conceptual framework of the heart has emerged. The heart is now viewed as a self-renewing organ in which myocyte regeneration occurs throughout the organism lifespan (Figure 1). Myocytes are the progeny of resident CSCs stored in niches. The niches control the turnover of myocardial cells and the growth, migration, and commitment of primitive cells that leave the niches to replace old, dying cells in the myocardium.25 Regeneration implies that dead cells are replaced by newly formed cells that differentiate and organize in a complex pattern, restoring the original structure of the lost tissue. In adulthood, this process occurs in its completeness during physiological cell turnover, in the absence of injury. It is unknown why damage interferes with the recapitulation of cell turnover and restitutio ad integrum of the organ. A plausible hypothesis is that inflammation at the site of injury opposes the orderly reconstitution and spatial arrangement of myocytes and coronary vessels.26 However, CSCs can be coaxed in vivo to home to the damaged area and promote the formation of parenchymal cells and vascular structures, resulting in recovery of ventricular performance.23,25
|
-sarcomeric actin, red) in fetal (B), neonatal (C), adult (D), and hypertrophied (E) rat heart. Mitotic myocytes (arrows) are shown in inserts. Bright blue denotes Ki67. Scale bars=10 µm; for methods, see references. |
Phenotype of CSCs |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
Investigators in several laboratories concur with the notion that the heart contains a compartment of undifferentiated cells with the characteristics of stem cells.6,8,15–20,23,25,27 However, the actual number of CSCs remains controversial. Reports in mice,17,25 rats,15 dogs,23 and humans8 indicate that there is 1 stem cell per
8000 to 20 000 myocytes, or 32 000 to 80 000 cardiac cells. Some investigators have reported that primitive cells represent 2% of all cells, ie, 2 per 25 myocytes, or 100 cardiac cells.16,18 This high value may reflect the contribution of endothelial progenitors.19,27 Discrepancy also exists in the identification of the stem cell antigens c-kit and Sca-1 on cardiac primitive cells. The presence of Sca-1 has been reported,16–19,25,27 whereas c-kit has been detected in 4 studies15,17,25,27 and found to be absent in another.16 c-kit–positive cells are an established component of the canine23 and human7,8,13,20 heart, and their activation leads to formation of new myocardium (Figure 2). The regenerative potential of c-kit–positive and Sca-1–positive cells after infarction15 or ischemia/reperfusion injury16,28 differs significantly; a robust regenerative response occurs with c-kit–positive cells,15,28 whereas little engraftment and repair take place with Sca-1–positive cells.16 Whether the modality of administration of cells, the animal model, and the properties of the injected cells are responsible for the different outcome is presently unclear.
|
The developing and adult heart typically contain a CSC pool that has the ability to efflux the Hoechst 33342 dye.6,16,18,19,29 Similar cells, which express an ATP-binding cassette transporter, have been identified in other organs and termed side-population (SP) cells.19,30 The classic member of this family is a P-glycoprotein that confers to the cells multidrug resistance by extruding anticancer drugs and rhodamine 123. These putative CSCs are 93% Sca-1–positive and appear to represent a subset, 1 per 10 000 cells, of the 2% Sca-1–positive cells in the mouse heart.16 According to a different study, however, SP cells comprise 2% of all cells (2 per 100 cardiac cells).18 Cardiac SP cells appear to express CD31 and form hematopoietic colonies in vitro.18 The presence of CD31, common to bone marrow SP cells,21,30 together with the peculiar growth behavior of these cells in vitro, raises questions concerning their actual origin and suggests possible colonization to the heart from the hematopoietic system.
Recently, a novel Sca-1–positive, Hoechst 33342 dye–low, and CD31-negative cardiac SP cell has been identified.19,29 The modest expression of c-kit in these cells was attributed to methodological limitations inherent in the enzymatic cleavage of this receptor during digestion of the myocardium and cell isolation.19 There is 1 SP cell per 30 000 cardiac cells in the mouse heart. CD31-negative cardiac SP cells acquire the myocyte lineage, reach the adult phenotype through a process mediated by cellular coupling with differentiated cardiomyocytes, and contract in vitro.19 These results strengthen the notion of a functional role for resident SP cells in the heart.
The Isl1 transcription factor is associated with the commitment to the myocyte lineage of cardiac cells that have lost their undifferentiated stem cell state. Isl1 and GATA4 are transcriptional coactivators of the myocyte transcription factor MEF2C.31 Homozygous deletion of Isl1 alters development of the mouse heart, affecting the atria, right ventricle, and outflow tract,32,33 and Isl1-positive cells may have implications for myocyte replacement in the newborn.34
Together, these observations are consistent with the notion that the heart possesses an intrinsic capacity for regeneration, but whether differences in the expression of surface antigens reflect CSC subclasses, which are functionally distinct, is difficult to ascertain. A direct comparison among stem cell phenotypes would require transplantation studies in which single CSCs are delivered to the chemically ablated or irradiated organ. To date, no information is available concerning the repopulating ability of individual CSCs in the depleted heart. Stem cell depletion is complex in solid organs, and currently, there are no protocols available to eliminate resident CSCs in the absence of extensive parenchymal damage and myocardial scarring.26 So far, only limited characterization of the in vitro properties of CSCs has been performed. However, these data do not answer the question whether the expression of 1 stem cell antigen versus another carries a greater or reduced regeneration potential for the diseased heart.
|
Classification of CSCs and Their Progeny |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
Information obtained so far on the phenotype of adult CSCs is incomplete. The nomenclature is imprecise, and frequently, cells with distinct growth behaviors are defined by the same terminology. Some comments may be helpful. CSCs are undifferentiated, lineage-negative cells that possess a high growth potential.6,15–20,23,25 At the single-cell level, CSCs are self-renewing, clonogenic,15,19,23 and capable of differentiating in mature progenies in vitro15–17,19,23 and in vivo.8,15,16,23,25 Stem cells divide rarely, whereas the committed, amplifying cells are the actual group of replicating cells. Stem cells in the bone marrow, some areas of the brain, skeletal muscle, and heart share in different proportions the stem cell–related antigens c-kit, MDR1, and Sca-1.8,23,25
We propose a classification of cardiac immature cells into 4 classes: CSCs, progenitors, precursors, and amplifying cells. These cell types can be viewed as subsequent steps in the progressive evolution from a more primitive to a more differentiated phenotype (Figure 3). The first 3 cell types express c-kit, MDR1, and Sca-1, whereas the last type no longer expresses these antigens. This relatively simple terminology defines the fundamental characteristics of CSCs and the classes of cells generated by their lineage commitment.
|
The recognition of lineage-negative CSCs and their progenies is technically demanding and complex in the rat,15 mouse,6,16–19,25 dog,23 and human8 heart. These cell categories can be identified in isolated cardiac cell preparations or in sections of atrial and ventricular myocardium. In both cases, this is accomplished by utilizing several mixtures of antibodies directly labeled by fluorochromes to avoid cross-reactivity and nonspecific staining.8,23 With histological approaches, major screening with cocktails of fluorescein-conjugated antibodies may be followed by immunostaining with indirect labeling; this approach requires the use of secondary antibodies. Additionally, it is necessary to achieve the level of resolution afforded by confocal microscopy.35 Contrary to common belief,2,36–38 confocal microscopy is the only method that permits quantitative measurement of the frequency and distribution of CSC classes in the myocardium.26,39 Fluorescence-activated cell sorting analysis is extremely efficient in separating cells in specific categories according to the expression of 1 or more surface epitopes,40,41 but the distinction between lineage-negative and committed cells requires the analysis of nuclear and cytoplasmic proteins. This can only be obtained by fixation of cells to make them permeable for the detection of intracellular components.42,43 Similar problems exist with immunolabeling. With either protocol, cell viability is lost, precluding further study.
Although stem cells have been known for quite some time, the importance of stem cell antigens in the growth and differentiation potential of these cells remains poorly understood.44–46 These limitations are not restricted to the heart and CSCs but also apply to stem cells in other organs, including the bone marrow. As indicated earlier, c-kit, MDR1, and Sca-1 are present not only on the surface of primitive cells but also in cells undergoing lineage differentiation, complicating recognition of the actual primitive cells in the population. Similarly, the detection of these antigens in cells collected by enzymatic digestion of the myocardium is highly dependent on the isolation protocol, which inevitably affects the yield, properties, and purity of the preparation, as well as the integrity of surface antigens. For this reason, some of the differences encountered in the characterization of CSCs and various subsets may be accounted for by technical difficulties inherent in the separation and collection of these cells from a solid organ.19
To gain insights into the functional implications that different CSC surface antigens may have in myocardial growth in large mammals, CSCs were isolated and characterized in the dog heart.23 Consistent with results in the mouse,25 rat,15 and human8 heart, canine CSCs expressing 3 surface antigens constitute the prevailing population, (60%); those expressing 2 antigens, the second most frequent fraction (25%); and those expressing 1 antigen, the least represented component (15%). CSCs with 1 epitope were equally distributed, nearly 5% for each surface antigen. The size of clones and subclones varies when CSCs express different epitopes (Figure 3).
Clones from c-kit–positive CSCs are 2.3-fold, 5.9-fold, and 7.6-fold larger than MDR1-, Sca-1–like-, and c-kit/MDR1/Sca-1–like-positive clones, respectively.23 When the same number of clonogenic cells, 100, from each of these clones is driven to growth and differentiation, the magnitude of the population of committed cells differs, depending on whether it develops from c-kit–, MDR1-, Sca-1–like-, or c-kit/MDR1/Sca-1–like-positive clonogenic cells. Over a period of 4 weeks, 1.05x106, 3.9x105, 2.4x105, and 1.6x105 differentiated cardiac cells are formed from c-kit–, MDR1-, Sca-1–like-, and c-kit/MDR1/Sca-1–like-positive clonogenic cells, respectively.23 Therefore, the ability of c-kit–positive cells to generate cardiac cell lineages is greater than that of MDR1-, Sca-1–like-, and c-kit/MDR1/Sca-1–like-positive cells. Clonogenic MDR1-positive cells produce more myocardial cells than do Sca-1–like- and c-kit/MDR1/Sca-1–like-positive cells. Although there is no appreciable difference in the relative proportion of myocytes formed by each clonogenic CSC class (myocytes, 50%; SMCs, 40%; and ECs, 10%), the aggregate number of myocytes, SMCs, and ECs created by the c-kit–positive cells is several-fold larger than that obtained from other CSC categories.23
Understanding the relation between stem cell antigens and growth characteristics of CSCs has important implications in the future implementation of CSC therapy in patients. A critical question that needs to be addressed is whether human c-kit–positive CSCs, followed by MDR1-positive cells, constitute the more powerful CSC classes for acute regeneration of myocytes and coronary vessels in the damaged heart. Sca-1–like- and c-kit/MDR1/Sca-1–like-positive CSCs may be less relevant for emergency need and may be implicated in the formation of coronary arterioles, capillary structures, and myocytes to compensate for a defective growth in the other stem cell populations. Alternatively, these latter 2 classes may be prevalently involved in the low physiological turnover of cardiac cells. These possibilities are not mutually exclusive.
|
CSCs and Cell Turnover |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
Researchers from 8 laboratories have shown that stem cells are present in the adult heart of small and large mammals, including humans.6–8,13,15–20,23,25,27,29 Despite these findings, the shift in paradigm from the heart as a postmitotic organ to a self-renewing organ has not yet occurred. At best, the heart is now viewed as an organ capable of some but severely limited regeneration.1,2,18,47 On the basis of this premise, strategies aimed at reversing the terminally differentiated state of myocytes have been proposed as an alternative intervention for the cellular repopulation of the diseased heart.48 In this section, we discuss the reasons for the unwillingness to lay to rest the old dogma and adopt a novel biological perspective of the heart. The new paradigm sees the heart as a highly dynamic organ in which old, poorly functioning myocytes and vascular SMCs and ECs are continuously replaced by activation and commitment of resident CSCs. The recognition of the mechanisms that regulate the physiological turnover of cardiac cells may offer a unique, unprecedented approach for cardiac repair. Potentiation of this naturally occurring process may become the most efficient and successful form of tissue reconstitution for the failing heart. In this scenario, exogenous expansion of autologous CSCs,15,16,20 bone marrow progenitor cells,35,49–53 and skeletal myoblasts54 for subsequent myocardial implantation55,56 would be seen as a secondary model of cell therapy and not as the primary method of choice. Similarly, the use of genetically manipulated, nonmalignant, nonimmunogenic embryonic stem cells57,58 would be envisioned only in extreme cases. Currently, embryonic stem cells are immunogenic59 and tumorigenic,60–62 precluding their clinical relevance in the near future.26
The reluctance to accept a reassessment of cardiac biology and pathology has its foundation on 4 major questions: (1) Are CSCs responsible for myocardial homeostasis and therefore, for an effective physiological replacement of dying cardiac cells, including cardiomyocytes? (2) Is the CSC pool activated after injury, and if so, does this lead to a relevant increase in the number of myocytes and coronary vessels? (3) If properly activated, are CSCs able to translocate to areas of damage, grow, and differentiate, thereby restoring the lost myocardium? (4) Assuming that the heart has a powerful growth reserve dictated by the CSC compartment, do aging and chronic heart failure reduce the pool of functionally competent CSCs, and if so, is this defect important in the development of end-stage failure? The answers to these questions will provide a framework for a cardiac paradigm that does not ignore the discovery of CSCs and their role in the life and death of the heart.
Cardiac homeostasis is regulated by the balance between old, senescent cardiac cells undergoing apoptosis/necrosis and the formation of new cells through the commitment of CSCs. CSCs are clustered in the atria and apex but are also present throughout the ventricular myocardium.25 An equivalent loss and generation of cardiomyocytes, vascular SMCs, and ECs would be expected to occur in the entire heart to preserve its equilibrium, before aging effects become apparent.10,63,64 Because of the conviction that myocytes cannot be replaced1,2 and that "adult" SMCs and ECs reenter the cell cycle and divide,65,66 independently from lineage specification of primitive cells, the possible function of CSCs in myocardial cell turnover has only been recently explored.
Information obtained so far is incomplete but strongly supports the notion that the heart contains a pool of replicating, lineage-negative CSCs, together with myocyte, SMC, and EC progenitors and precursors, and highly proliferating amplifying cells. The retroviral tagging of undifferentiated cells in vivo or in vitro before their intramyocardial injection has demonstrated that developing and mature cells are the progeny of activated CSCs.15,25,28 A similar analysis could not be obtained in the human heart. All of these cell classes have been identified in the ventricular myocardium, however, suggesting that a similar growth behavior occurs in the human heart (Figure 4) and that it involves CSC multilineage commitment and differentiation.7,8,10–13 Myocytes, and SMCs and ECs in coronary vessels, die continuously, and the constant replacement of cells preserves the integrity of the tissue and the function of the organ. Whether cell death triggers regeneration or whether regeneration activates cell death is not known, but cellular aging with loss of replicating cells is invariably associated with initiation of the death pathway.67–69
|
In recent work,7,8,10–13 the numbers of cycling and noncycling lineage-negative CSCs, myocyte progenitors/precursors, cycling amplifying myocytes, terminally differentiated nonaged myocytes, and senescent myocytes have been measured in the human heart. Similarly, the mitotic index and Ki67 and MCM5 labeling of myocyte nuclei have been obtained in humans.7,8,11,12 On the basis of the fact that mitosis is a rapid process,70 the duration of the cell cycle in forming myocytes has been estimated previously to be 25 hours.7,11,12 Additionally, the ratio of progenitors to precursors to amplifying cells to lineage-negative CSCs was determined8 to compute the number of transit generations from the uncommitted state to terminal differentiation, ie, 7 rounds of the cell cycle.71 Together, these data define the rate of turnover (death/formation) of the myocyte population. In the normal human heart, there are 5x109 parenchymal cells in the left ventricle inclusive of the interventricular septum,72,73 and 3x106 terminally differentiated myocytes are generated per day (Table) by commitment and growth of CSCs.7,8,11,12 This degree of myocyte formation ensures that the entire cell population of the heart is replaced approximately every 4.5 years. Thus, parenchymal cells cannot live, as is generally believed, as long as the organism, 80 years.74 The human heart replaces completely its myocyte population 18 times during the course of life, independently from cardiac diseases.
|
There is a remarkable balance between the formation and loss of myocytes physiologically (Table). It has been shown that in the normal adult human heart, cell death by apoptosis/necrosis75 accounts for the loss of 3x106 myocytes per day, a value essentially identical to that of regenerated myocytes. The rate of cell death is calculated from the measurement of apoptosis and necrosis of myocytes,75,76 together with the duration of apoptosis, 3 hours,77 and necrosis, 24 hours.78 If the heart were postmitotic and dying myocytes were not constantly replaced, the entire organ would disappear in 4.5 years. These conservative estimates project a remarkably different image of the human heart, in sharp contrast to the contention that this organ has a poor ability to regenerate myocytes, inadequate for significant myocardial reconstitution.1,2,79
Whether SMCs and ECs organized in vascular structures experience higher or lower turnover rates than do myocytes in mammals is difficult to predict. At present, only scattered information is available on the growth and death of these cell populations, precluding a meaningful analysis of their short- and long-term fate in the control and pathological heart. However, EC and SMC progenitors and precursors are easily detectable in the human,7,8 dog,23 rat,15,28 and mouse25 myocardium. These observations support the notion that lineage specification of CSCs contributes to the formation of coronary vessels and the replacement of ECs and SMCs within the vascular wall. However, functionally competent ECs and SMCs can reenter the cell cycle and divide, and this growth reserve represents a relevant component of angiogenesis and/or cell turnover.65,66 Importantly, circulating endothelial progenitor cells are a powerful source of vasculogenesis.50,51,80 How CSCs, replicating vascular SMCs, and endothelial progenitor cells interplay in the homeostasis and growth of coronary vessels remains a critical, unanswered question.
In summary, the adult heart is not a static but a very dynamic organ whose homeostasis is governed by a compartment of multipotent CSCs, which continuously repopulate the myocardium, replacing parenchymal cells and vascular SMCs and ECs that die by apoptosis/necrosis. CSCs provide the adult heart with a growth reserve that can restore a large number of myocytes and replace the entire myocyte compartment several times during the course of life in animals and humans. The notion that the heart retains the capacity to regenerate cardiomyocytes, coronary resistance arterioles, and capillary structures throughout life has far-reaching implications.
|
Stem Cells and Cardiac Repair |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
The adult heart is well equipped to sustain organ homeostasis, which efficiently preserves the integrity of the tissue during physiological cell turnover. The equilibrium between the rates of dying and forming myocytes suggests that the CSC compartment senses signals from cells undergoing apoptosis or necrosis, which in turn activate the growth and commitment of primitive cells replacing dying myocytes. More complex is the issue of whether the heart has the intrinsic ability to regenerate large quantities of myocytes after myocardial infarction. The setting of myocardial infarction has been cited as an indisputable argument against myocyte regeneration and significant growth reserve of the adult heart.81 Although this logic is deeply ingrained in the clinical and scientific community, it falls short for several reasons. The outcome of infarction is essentially identical in all organs of the organism, regardless of whether the parenchymal and nonparenchymal cells are able to enter the cell cycle and divide. The presence of stem cells does not prevent the inevitable evolution of the infarct with scar formation. Occlusion of a major conductive artery or large branch results in loss of tissue in the skin, kidney, intestine, brain, liver, and reproductive organs,82–85 in a manner identical to the heart.86 This general outcome of ischemic injury is dictated by 2 crucial factors: (1) Stem cells within the infarct die, as do all other cells deprived of oxygen supply, and (2) resident stem cells cannot migrate from the viable tissue to the damaged area, home, grow, and differentiate to replace the dead cell lineages. CSC death within the infarct has been well documented,23,25 but viable, cycling CSCs as well as replicating myocyte progenitors and precursors, in combination with highly dividing amplifying myocytes, are commonly found7,8,12,23,25 throughout the surviving myocardium (Figure 5). These observations provide an explanation for the lack of myocardial regeneration within the infarct and the intense myocyte formation in the nonischemic region of the ventricular wall.8,11,12 The important point is that the behavior of the heart is not different from that of other self-renewing organs, including the bone marrow, skin, intestine, brain, kidney, and liver.
|
Although myocardial infarcts do not regenerate spontaneously, the endogenous repair mechanisms of the heart can be manipulated and exploited to accomplish this objective. Thus, the critical question is whether the growth reserve of the adult heart is sufficient to reconstitute acute and massive losses of myocardium. To resolve this issue, the ability to form parenchymal cells needs to be examined in 2 distinct regions of the diseased heart, the nondamaged and damaged myocardium.7,8,10–13,15,16,23,25 The latter can only be measured by interventions that promote the translocation of CSCs from the surviving to the dead tissue and, by necessity, can only be determined experimentally, because similar strategies have not been developed in humans.
In humans, myocyte formation within the noninjured tissue is dramatically potentiated in acute and chronic heart failure, and this increased generation of myocytes is sustained by enhanced replication and lineage commitment of CSCs. Patients who die shortly after infarction8,12 give us a good indication of the maximal regeneration potential of the human heart. An infarcted ventricle with 190 g of viable myocardium8 and a myocyte mitotic index12 of 500/106 can create 2.20x108 myocytes per day (Table). This value is 70-fold higher than the baseline turnover rate (see earlier sections). If this magnitude of myocyte growth were to persist, a 40% infarct that reflects a loss of 2x109 myocytes would be repaired in 10 days. In end-stage postinfarction cardiomyopathy, there is an 70% reduction in myocyte mitotic index,11 to a value of 140/106. However, the viable ventricular muscle mass is increased to 260 g.8 These factors lead to the generation of 3.4x107 myocytes per day, which is 11-fold higher than physiological turnover.
Therefore, the severely decompensated human heart possesses a relevant growth reserve, which is, however, restricted to the noninfarcted region of the wall. Additionally, ongoing myocyte death in the surviving myocardium comprises 1.80x108 myocytes acutely after infarction (authors’ unpublished data, 2006) and 108 myocytes in end-stage postinfarction heart failure.75 On the basis of these observations, myocyte regeneration modestly exceeds myocyte death acutely after infarction, but myocyte replacement is markedly less than myocyte death in the long term. Thus, myocyte death significantly interferes with the recovery of structure and function after an acute infarct and results in loss of myocardium in long-term ischemic heart disease (Table). In the early phases of postinfarct myopathy, growth of the spared myocardium is not associated with invasion and repair of the infarcted area that conditions the chronic alterations in size, shape, and performance of the heart. The time-dependent worsening of cardiac anatomy and hemodynamics can only be prevented and reversed if the dead tissue is restored with new, functionally competent myocardium. In its absence, myocyte hypertrophy occurs and cellular enlargement depresses ventricular function further. Regeneration attenuates the load on the surviving myocardium and attenuates or corrects cavitary dilation and wall thinning. Successful strategies in this direction have been developed in the mouse25 and dog23 heart. Local growth factor activation of CSCs within the myocardium can rescue mice with large infarcts (Figure 6), in the long term leading to reconstitution of the infarcted ventricular wall, normalization of the ventricular mass-to–chamber volume ratio, and acquisition of the adult phenotype by a fraction of newly formed myocytes.25
|
|
CSC Aging and Death |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
The evidence reviewed earlier indicates that the heart is a self-renewing organ and that the growth of its parenchymal cells is regulated by the CSC compartment and by the ability of CSCs to self-renew and differentiate. Telomeres are chromatin structures composed of tandem G-rich repeats bound to an array of proteins that cap the ends of chromosomes and are critical for chromosomal stability and cell viability.67 Proliferation of human stem cells is dependent on a functional telomere.87 Telomere shortening coupled to cell division in the absence of telomerase activity is 1 of the major causes of telomere dysfunction in human cells. Severe telomeric shortening to a critical length triggers chromosome end-to-end fusion, which affects cell replication and survival.67,87 Telomerase prevents telomere erosion and chromosomal instability by protecting against the loss of DNA at the chromosomal ends during cell division, which, with time and repeated doublings, results in irreversible growth arrest, cellular senescence, and apoptosis.9,10 Typically, stem cells undergo replicative senescence with loss of self-renewing capacity and commitment and differentiation.87 Telomeric shortening affects CSCs and myocytes in the aged and diseased heart (Figure 7).
|
The length of telomeres is a good predictor of the regenerative potential of a cell,87,88 and cycling human CSCs express telomerase. This morphological characteristic has its molecular equivalent in telomerase activity.7–9 These results are consistent with the notion that control of telomere length in CSCs is regulated by telomerase and not by alternative telomere-lengthening mechanisms.89 However, other factors are crucial for telomere maintenance. The loss of integrity of telomere structure, which is composed of repetitive sequences of DNA and proteins, significantly conditions telomeric shortening. Telomeres are protected by a complex of proteins, including TRF1 and its partners tankyrase and TIN-2, TRF2, poly(ADP-ribose) polymerase, DNA-dependent protein kinase, Ku80, Ku70, and Pot1.8,90 Therefore, replicative senescence of CSCs can be induced by changes in the protected status of telomeres rather than by a pure loss of telomeric DNA. In myocardial aging and chronic heart failure, CSCs are characterized by telomere dysfunction with alterations in telomeric binding proteins.8,10 These molecular modifications are accompanied by increased expression of p14ARF, p16INK4a, phospho-Ser-15-p53, and p53; p14ARF inhibits p53 degradation, and p16INK4a inhibits cdk4 and cdk6, blocking cells at the G0-G1 boundary. Moreover, p53 inhibits the cell cycle at the G1-S or G2-M checkpoint. Bmi-1, which is a negative modulator of the age-associated genes p14ARF and p16INK4a, decreases in CSCs in chronic heart failure.91 Telomere dysfunction, cellular senescence, and the expression of genes that interfere with cell replication and that activate cell death are enhanced in CSCs of hearts suffering from aging and end-stage failure. Together, these factors result in the loss of functionally competent CSCs, which can no longer reenter the cell cycle and divide because they have reached replicative senescence.8,10,63,64 Telomere dysregulation, in combination with the expression of p53 and p16INK4a, activates the death program, further decreasing the size of the CSC pool in the heart. Despite cellular senescence and death, however, the old heart10 and the chronically decompensated heart8 possess a number of CSCs that retain the ability to divide and differentiate. These CSCs have long telomeres, express telomerase and cycling proteins such as Ki67 and MCM5, and are p53- and p16INK4a-negative (Figure 8). Whether these CSCs maintain their youth and self-renewing property or whether they represent a residual pool of defective old cells is currently unknown.
|
The rate of organ aging depends on the pace of cell-autonomous processes resulting in the accumulation of older cells with impaired function.92 This accumulation is in turn linked to a decline in the capacity of the organ to replace old cells with better-functioning, younger cells. Therefore, aging of the heart is defined at the level of the controlling cell, ie, the CSC. CSC aging decreases the pool size of functionally competent stem cells, impairing the compensatory growth mechanisms of the heart and its ability to sustain sudden increases in workload and ventricular performance.8,10 These limitations are apparent in aging human hearts in which ischemic injury has much more dramatic effects in terms of morbidity and mortality than in younger individuals.93 In the elderly, premature cardiac aging manifests itself with loss of CSC growth, CSC apoptosis, and heart failure.10 Similarly, chronic cardiac failure of ischemic and nonischemic origin is characterized by a remarkable increase in the number of senescent CSCs and senescent, poorly contracting, hypertrophied myocytes.7,8 Regeneration is activated, but the long-term outcome of CSC division is telomeric shortening, replicative senescence, cell death, reduction of the stem cell pool, and ultimately, exhaustion of their growth reserve.
|
Conclusions |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
In self-renewing organs, cell number is controlled by the stem cell compartment. A good example of this paradigm is found in the hematopoietic system. Despite the fact that proliferation and self-renewal of HSCs are limited and dependent on telomere length and telomerase activity, these cells may not reach their intrinsic limits during the organism’s lifespan.94 The turnover of mature blood cells is maintained in old age, although alterations in gene expression have been reported.95 Conversely, the turnover of myocytes and vascular SMCs and ECs is not preserved in the aging heart of mammals, including humans.72,73 Rarefaction of the coronary vasculature and myocyte loss characteristically occur in men, whereas the number of parenchymal cells is not reduced in age-matched women.96 This growth defect occurs in women nearly a decade later than in men. When telomere attrition and replicative senescence of CSCs become apparent, myocardial aging and heart failure develop in humans.10 Similarly, CSCs cannot supply the acutely and chronically decompensated human heart with the necessary number of cardiomyocytes and vascular structures, so the diseased heart is composed of a reduced number of parenchymal cells and coronary vessels. Hypertrophied, senescent myocytes accumulate, and the ratio of old to young cells severely increases; this condition is present in CSCs and in other cardiac lineages. Equivalent conditions to the aging and failing heart are found HSC disorders, such as aplastic anemia and myelodysplastic syndromes.97,98 These pathological conditions cause bone marrow failure, which manifests itself with a drastic decline in HSCs and in the bone marrow’s ability to produce mature blood cells. This is mimicked in the aged and decompensated heart in which the balance between cell loss and cell formation is altered in favor of the former, indicating CSC failure.8,10
Thus, heart failure and the myopathy of aging share a common underlying cellular alteration that involves the stem cell compartment. Telomeric dysregulation and shortening lead to growth arrest and apoptosis of CSCs, and these processes negatively affect the creation of parenchymal cells and coronary vessels in the myocardium. Additionally, CSCs are not equipped to sense signals from areas of damage that could promote their recruitment and regeneration potential, although they can be coaxed to home to sites of injury, where they can restore dead myocardium. However, their growth and survival, together with their translocation and speed of locomotion, are impaired with aging and most likely with chronic heart failure, and these defects are the consequence of downregulation of the local c-Met–hepatocyte growth factor and insulin-like growth factor-1/insulin-like growth factor receptor systems.23,64 Although CSCs are efficient in preserving organ homeostasis and cell turnover, the decompensated heart is characterized by a loss of myocytes and vascular structures that cannot be counteracted by the activation and differentiation of CSCs, which undergo progressive replicative senescence, leading to a dramatic reduction of the stem cell compartment. In this sense, cardiac aging and chronic heart failure can be viewed as stem cell disorders. It is hoped that the new paradigm of cardiac biology and an improved understanding of the fundamental role of CSCs in cardiac physiology and pathophysiology will promote the development of novel therapeutic strategies for alleviating heart failure and perhaps even for preventing cardiac senescence.
|
Acknowledgments |
|---|
Disclosures
None.
|
References |
|---|
|
TopIntroductionThe Heart Is a...Phenotype of CSCsClassification of CSCs and...CSCs and Cell TurnoverStem Cells and Cardiac...CSC Aging and DeathConclusionsReferences |
|---|
1. Nadal-Ginard B, Mahdavi V. Molecular basis of cardiac performance. J Clin Invest. 1989; 84: 1693–1700.[Medline] [Order article via Infotrieve]
2. Chien KR. Stem cells: lost in translation. Nature. 2004; 428: 607–608.[CrossRef][Medline] [Order article via Infotrieve]
3. Olson EN, Schneider MD. Sizing up the heart: development redux in disease. Genes Dev. 2003; 17: 1937–1956.
4. Solomon SD, Zelenkofske S, McMurray JJV, Finn PV, Velazquez E, Ertl G, Harsanyi A, Rouleau JL, Maggioni A, Kober L, White H, Van de Werf F, Pieper K, Califf RM, Pfeffer MA. Sudden death in patients with myocardial infarction and left ventricular dysfunction, heart failure, or both. N Engl J Med. 2005; 352: 2581–2588.
5. Keegan BR, Feldman JL, Begemann G, Ingham PW, Yelon D. Retinoic acid signaling restricts the cardiac progenitor pool. Science. 2005; 307: 247–249.
6. Hierlihy AM, Seale P, Lobe CG, Rudnicki MA, Megeney LA. The post-natal heart contains a myocardial stem cell population. FEBS Lett. 2002; 530: 239–243.[CrossRef][Medline] [Order article via Infotrieve]
7. Urbanek K, Quaini F, Tasca G, Torella D, Castaldo C, Nadal-Ginard B, Leri A, Kajstura J, Quaini E, Anversa P. Intense myocyte formation from cardiac stem cells in human cardiac hypertrophy. Proc Natl Acad Sci U S A. 2003; 100: 10440–10445.
8. Urbanek K, Torella D, Sheikh F, De Angelis A, Nurzynska D, Silvestri F, Beltrami CA, Bussani R, Beltrami AP, Quaini F, Bolli R, Leri A, Kajstura J, Anversa P. Myocardial regeneration by activation of multipotent cardiac stem cells in ischemic heart failure. Proc Natl Acad Sci U S A. 2005; 102: 8692–8697.
9. Leri A, Barlucchi L, Limana F, Deptala A, Darzynkiewicz Z, Hintze TH, Kajstura J, Nadal-Ginard B, Anversa P. Telomerase expression and activity are coupled with myocyte proliferation and preservation of telomeric length in the failing heart. Proc Natl Acad Sci U S A. 2001; 98: 8626–8631.
10. Chimenti C, Kajstura J. Torella D, Urbanek K, Heleniak H. Colussi C, Di Meglio F, Nadal-Ginard B, Frustaci A, Leri A, Maseri A, Anversa P. Senescence and death of primitive cells and myocytes lead to premature cardiac aging and heart failure. Circ Res. 2003; 93: 604–613.
11. Kajstura J, Leri A, Finato N, Di Loreto C, Beltrami CA, Anversa P. Myocyte proliferation in end-stage cardiac failure in humans. Proc Natl Acad Sci U S A. 1998; 95: 8801–8805.
12. Beltrami AP, Urbanek K, Kajstura J, Yan SM, Finato N, Bussani R, Nadal-Ginard B, Silvestri F, Leri A, Beltrami CA, Anversa P. Evidence that human cardiac myocytes divide after myocardial infarction. N Engl J Med. 2001; 334: 1750–1757.
13. Quaini F, Urbanek K. Beltrami AP, Finato, N. Beltrami CA, Nadal-Ginard B, Kajstura J. Leri A, Anversa P. Chimerism of the transplanted heart. N Engl J Med. 2002; 346: 5–15.
14. Schwartz RS, Curfman GD. Can the heart repair itself? N Engl J Med. 2002; 364: 2–4.
15. Beltrami AP, Barlucchi L, Torella D, Baker M, Limana F, Chimenti S, Kasahara H, Rota M, Musso E, Urbanek K, Leri A, Kajstura J, Nadal-Ginard B, Anversa P. Adult cardiac stem cells are multipotent and support myocardial regeneration. Cell. 2003; 114: 763–766.[CrossRef][Medline] [Order article via Infotrieve]
16. Oh H, Bradfute SB, Gallardo TD, Nakamura T, Gaussin V, Mishina Y, Pocius J, Michael LH, Behringer RR, Garry DJ, Entman NL, Schneider MD. Cardiac progenitor cells from adult myocardium: homing, differentiation, and fusion after infarction. Proc Natl Acad Sci U S A. 2003; 100: 12313–12318.
17. Matsuura K, Nagai T, Nishigaki N, Oyama T, Nishi J, Wada H, Sano M, Toko H, Akazawa H, Sato T, Nakaya H, Kasanuki H, Komuro I. Adult cardiac Sca-1-positive cells differentiate into beating cardiomycytes. J Biol Chem. 2004; 279: 11384–11391.
18. Martin CM, Meeson AP, Robertson SM, Hawke TJ, Richardson JA, Bates S, Goetsch SC, Gallardo TD, Garry DJ. Persistent expression of the ATP-binding cassette transporter, Abcg2, identifies cardiac SP cells in the developing and adult heart. Dev Biol. 2004; 265: 262–275.[CrossRef][Medline] [Order article via Infotrieve]
19. Pfister O, Mouquet F, Jain M, Summer R, Helmes M, Fine A, Colucci WS, Liao R. CD31- but not CD31+ cardiac side population cells exhibit functional cardiomyogenic differentiation. Circ Res. 2005; 97: 52–61.
20. Messina E, De Angelis L, Frati G, Morrone S, Chimenti S, Fiordaliso F, Salio M, Battaglia M, Latronico MVG, Coletta M, Vivarelli E, Frati L, Cossu G, Giacomello A. Isolation and expansion of adult cardiac stem cells from human and murine heart. Circ Res. 2004; 95: 911–921.
21. Jackson KA, Majka SM, Wang H, Pocius J, Hartley CJ, Majesky MW, Entman ML, Michael LH, Hirschi KK, Godell MA. Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells. J Clin Invest. 2001; 107: 1395–1402.[CrossRef][Medline] [Order article via Infotrieve]
22. Wagers AJ, Weissman IL. Plasticity of adult stem cells. Cell. 2004; 116: 639–648.[CrossRef][Medline] [Order article via Infotrieve]
23. Linke A, Muller P, Nurzynska D, Casarsa C, Torella D, Nascimbene A, Castaldo C, Cascapera S, Bohm M, Quaini F, Urbanek K, Leri A, Hintze TH, Kajstura J, Anversa P. Stem cells in the dog heart are self-renewing, clonogenic, and multipotent and regenerate infarcted myocardium, improving cardiac function. Proc Natl Acad Sci U S A. 2005; 102: 8966–8971.
24. Soonpaa MH, Field LJ. Survey of studies examining mammalian cardiomyocyte DNA synthesis. Circ Res. 1998; 83: 15–26.
25. Urbanek K, Rota M, Cascapera S, Bearzi C, Nascimbene A, De Angelis A, Hosoda T, Chimenti S, Baker M, Limana F, Nurzynska D, Torella D, Rotatori F, Rastaldo R, Musso E, Quaini F, Leri A, Kajstura J, Anversa P. Cardiac stem cells possess growth factor-receptor systems that following activation regenerate the infarcted myocardium improving ventricular function and long-term survival. Circ Res. 2005; 97: 663–673.
26. Leri A, Kajstura J, Anversa P. Cardiac stem cells and mechanisms of myocardial regeneration. Physiol Rev. 2005; 85: 1373–1416.
27. Rosenblatt-Velin N, Lepore MG, Cartoni C, Beermann F, Pedrazzini T. FGF-2 controls the differentiation of resident cardiac precursors into functional cardiomyocytes. J Clin Invest. 2005; 115: 1724–1733.[CrossRef][Medline] [Order article via Infotrieve]
28. Dawn B, Stein AB, Urbanek K, Rota M, Whang B, Rastaldo R, Torella D, Tang XL, Rezazadeh A, Kajstura J, Leri A, Hunt G, Varma J, Prabhu SD, Anversa P, Bolli R. Cardiac stem cells delivered intravascularly traverse the vessel barrier, regenerate infarcted myocardium, and improve cardiac function. Proc Natl Acad Sci U S A. 2005; 102: 3766–3771.
29. Mouquet F, Pfister O, Jain M, Oikonomopoulos A, Ngoy S, Summer R, Fine A, Liao R. Restoration of cardiac progenitor cells after myocardial infarction by self-proliferation and selective homing of bone marrow-derived stem cells. Circ Res. 2005; 97: 1090–1092.
30. Zhou S, Schuetz JD, Bunting KD, Colapietro AM, Sampath J, Morris JJ, Lagutina I, Grosveld GC, Osawa M, Nakauchi H, Sorrentino BP. The ABC transporter Bcrp1/ABCG2 is expressed in a wide variety of stem cells and is a molecular determinant of the side-population phenotype. Nat Med. 2001; 7: 1028–1034.[CrossRef][Medline] [Order article via Infotrieve]
31. Dodou E, Verzi MP, Anderson JP, Xu SM, Balck BL. Mef2c is a direct transcriptional target of ISL1 and GATA factors in the anterior heart field during mouse embryonic development. Development. 2004; 131: 3931–3942.
32. Yuan S, Schoenwolf GC. Islet-1 marks the early heart rudiments and is asymmetrically expressed during early rotation of the foregut in the chick embryo. Anat Rec. 2000; 260: 204–207.[CrossRef][Medline] [Order article via Infotrieve]
33. Cai CL, Laing X, Shi Y, Chu PH, Pfaff SL, Chen J, Evans S. Is11 identifies a cardiac progenitor population that proliferates prior to differentiation and contributes a majority of cells to the heart. Dev Cell. 2003; 5: 877–889.[CrossRef][Medline] [Order article via Infotrieve]
34. Laugwitz KL, Moretti A, Lam J, Gruber P, Chen Y, Woodard S, Lin LZ, Cai CL, Lu MM, Reth M, Platoshyn O, Yuan JX, Evans S, Chien KR. Postnatal is11+ cardioblasts enter fully differentiated cardiomyocyte lineages. Nature. 2005; 433: 585–587.[CrossRef][Medline] [Order article via Infotrieve]
35. Kajstura J, Rota M, Whang B, Cascapera S, Hosoda T, Bearzi C, Nurzynska D, Kasahara H, Zias E, Bonafe M, Nadal-Ginard B, Torella D, Nascimbene A, Quaini F, Urbanek K, Leri A, Anversa P. Bone marrow cells differentiate in cardiac cell lineages after infarction independently of cell fusion. Circ Res. 2005; 96: 127–137.
36. Laflamme MA, Myerson D, Saffitz JE, Murry CE. Evidence for cardiomyocyte repopulation by extracardiac progenitors in transplanted human hearts. Circ Res. 2002; 90: 634–640.
37. Taylor DA, Hruban R, Rodriguez ER, GoldSchmidt-Clermont PJ. Cardiac chimerism as a mechanism for self-repair: does it happen and if so to what degree? Circulation. 2002; 106: 2–4.
38. No consensus on stem cells. Nature. 2004; 428: 587.[Medline] [Order article via Infotrieve]
39. Anversa P, Leri A, Kajstura J. Cardiac regeneration. J Am Coll Cardiol. In press.
40. Ferrero D, Gabbianelli M. Peschle C, Lange B, Rovera G. Surface phenotypes of human hemopoietic progenitor cells defined by monoclonal antibodies. Blood. 1985; 66: 496–502.
41. Askura A, Seale P, Girgis-Gabardo A, Rudnicki MA. Myogenic specification of side population cells in skeletal muscle. J Cell Biol. 2002; 159: 123–134.
42. Harvey KA, Siddiqui RA, Jansen J, Akard LP, Thompson JM, Cui Y, Chang Q, English D. Growth factor induction of cytosolic protein tyrosine kinase activity in human haemopoietic progenitor cells isolated by flow cytometry. Br J Haematol. 1996; 93: 515–526.[CrossRef][Medline] [Order article via Infotrieve]
43. Groeneveld K, te Marvelde JG, van den Beemd MW, Hooijkaas H, van Dongen JJ. Flow cytometric detection of intracellular antigens for immunophenotyping of normal and malignant leukocytes. Leukemia. 1996; 10: 1383–1389.[Medline] [Order article via Infotrieve]
44. Kondo M. Wagers AJ, Manz MG, Prohaska SS, Scherer DC, Beilhack GF, Shizuru JA, Weissman IL. Biology of hematopoietic stem cells and progenitors: implications for clinical application. Annu Rev Immunol. 2003; 21: 759–806.[CrossRef][Medline] [Order article via Infotrieve]
45. Davey RE, Zandstra PW. Signal processing underlying extrinsic control of stem cell fate. Curr Opin Hematol. 2004; 11: 95–101.[CrossRef][Medline] [Order article via Infotrieve]
46. Cai J. Weiss ML, Rao MS. In search of ‘stemness.’ Exp Hematol. 2004; 32: 585–598.[CrossRef][Medline] [Order article via Infotrieve]
47. Dimmeler S, Zeiher AM, Schneider MD. Unchain my heart: the scientific foundations of cardiac repair. J Clin Invest. 2005; 115: 572–583.[CrossRef][Medline] [Order article via Infotrieve]
48. Pasumarthi KB, Nakajima H, Nakajima HO, Soonpaa MH, Field LJ. Targeted expression of cyclin D2 results in cardiomyocyte DNA synthesis and infarct regression in transgenic mice. Circ Res. 2005; 96: 110–118.
49. Orlic D, Kajstura J, Chimenti S, Jakoniuk I, Anderson SM, Li B, Pickel J, McKay R, Nadal-Ginard B, Bodine DM, Leri A, Anversa P. Bone marrow cells regenerate infarcted myocardium. Nature. 2001; 420: 701–705.
50. Losordo DW, Dimmeler S. Therapeutic angiogenesis and vasculogenesis for ischemic disease, part II: cell-based therapies. Circulation. 2004; 109: 2692–2697.
51. Losordo DW, Dimmeler S. Therapeutic angiogenesis and vasculogenesis for ischemic disease, part I: angiogenic cytokines. Circulation. 2004; 109: 2487–2491.
52. Gnecchi M, He H, Liang OD, Melo LG, Morello F, Mu H, Noiseux N, Zhang L, Pratt RE, Ingwall JS, Dzau VJ. Paracrine action accounts for marked protection of ischemic heart by Akt-modified mesenchymal stem cells. Nat Med. 2005; 11: 367–368.[CrossRef][Medline] [Order article via Infotrieve]
53. Yoon YS, Wecker A, Heyd L, Park JS, Tkebuchava T, Kusano K, Hanley A, Scadova H, Qin G, Cha DH, Johnson KL, Aikawa R, Asahara T, Losordo DW. Clonally expanded novel multipotent stem cells from human bone marrow regenerate myocardium after myocardial infarction. J Clin Invest. 2005; 115: 326–338.[CrossRef][Medline] [Order article via Infotrieve]
54. Wollert KC, Drexler H. Clinical applications of stem cells for the heart. Circ Res. 2005; 96: 151–163.
55. Korbling M, Estrov Z. Adult stem cells for tissue repair: a new therapeutic concept? N Engl J Med. 2003; 349: 570–582.
56. Rosenthal N. Prometheus’s vulture and the stem-cell promise. N Engl J Med. 2003; 349: 267–274.
57. Orkin SH, Morrison SJ. Stem-cell competition. Nature. 2002; 418: 25–27.[CrossRef][Medline] [Order article via Infotrieve]
58. Mayhall EA, Paffett-Lugassy N, Zon LI. The clinical potential of stem cells. Cell Biol. 2004; 16: 713–720.
59. Kofidis T, Debruin JL, Tanaka M, Zwierzchoniewska M, Weissman I, Fedoseyeva E, Haverich A, Robbins RC. They are not stealthy in the heart: embryonic stem cells trigger cell infiltration, humoral and T-lymphocyte-based host immune response. Eur J Cardiothorac Surg. 2005; 28: 461–466.
60. Erdo F, Buhrle C, Blunk J. Hoehn M, Xia Y, Fleischmann B, Focking M, Kustermann E, Kolossov E, Hescheler J, Hossmann KA, Trapp T. Host-dependent tumorigenesis of embryonic stem cell transplantation in experimental stroke. J Cereb Blood Flow Metab. 2003; 23: 780–785.[CrossRef][Medline] [Order article via Infotrieve]
61. Kofidis T, de Bruin JL, Yamane T, Tanaka M, Lebl DR, Swijnenburg RJ, Weissman IL, Robbins RC. Stimulation of paracrine pathways with growth factors enhances embryonic stem cell engraftment and host-specific differentiation in the heart after ischemic myocardial injury. Circulation. 2005; 111: 2486–2493.
62. Laflamme MA, Murry CE. Regenerating the heart. Nat Biotechnol. 2005; 23: 845–856.[CrossRef][Medline] [Order article via Infotrieve]
63. Torella D, Rota M, Nurzynska D, Musso E, Monsen A, Shiraishi I, Zias E, Walsh K, Rosenzweig A. Sussman MA, Urbanek K, Nadal-Ginard B, Kajstura J, Anversa P, Leri A. Cardiac stem cell and myocyte aging, heart failure, and insulin-like growth factor-1 overexpression. Circ Res. 2004; 94: 514–524.
64. Sussman MA, Anversa P. Myocardial aging and senescence: where have the stem cells gone? Annu Rev Physiol. 2004; 66: 29–48.[CrossRef][Medline] [Order article via Infotrieve]
65. Thyberg J. Differentiated properties and proliferation of arterial smooth muscle cells in culture. Int Rev Cytol. 1996; 169: 183–265.[Medline] [Order article via Infotrieve]
66. Staton CA, Stribbling SM, Tazzyman S, Hughes R, Brown NJ, Lewis CE. Current methods for assaying angiogenesis in vitro and in vivo. Int J Exp Pathol. 2004; 85: 233–248.[CrossRef][Medline] [Order article via Infotrieve]
67. Leri A, Franco S, Zacheo A, Barlucchi L, Chimenti S, Limana F, Nadal-Ginard B, Kajstura J, Anversa P, Blasco MA. Ablation of telomerase and telomere loss leads to cardiac dilatation and heart failure associated with p53 upregulation. EMBO J. 2003; 22: 131–139.[CrossRef][Medline] [Order article via Infotrieve]
68. Suh Y. Cell signaling in aging and apoptosis. Mech Ageing Dev. 2002; 23: 881–890.
69. Soti C, Sreedhar AS, Csermely P. Apoptosis, necrosis and cellular senescence: chaperone occupancy as a potential switch. Aging Cell. 2003; 2: 39–45.[CrossRef][Medline] [Order article via Infotrieve]
70. Antonio C, Ferby I, Wilhelm H, Jones M, Karsenti E. Nebreda AR, Vernos I. Xkid, a chromokinesin required for chromosome alignment on the metaphase plate. Cell. 2000; 102: 425–435.[CrossRef][Medline] [Order article via Infotrieve]
71. Lehrer MS, Sun TT, Lavker RM. Strategies of epithelial repair: modulation of stem cell and transit amplifying cell proliferation. J Cell Sci. 1998; 111: 2867–2875.[Abstract]
72. Olivetti G, Melissari M, Capasso JM, Anversa P. Cardiomyopathy of the aging human heart. Circ Res. 1991; 68: 1560–1568.
73. Olivetti G, Giordano G, Carradi D, Melissari M, Lagrasta C, Gambert SR, Anversa P. Gender differences and aging: effects on the human heart. J Am Coll Cardiol. 1995; 26: 1068–1079.[Abstract]
74. Sanderson WC, Scherbov S. Average remaining lifetimes can increase as human populations age. Nature. 2005; 435: 811–813.[CrossRef][Medline] [Order article via Infotrieve]
75. Guerra S, Leri A, Wang X, Finato N, Di Loreto C, Beltrami CA, Kajstura J, Anversa P. Myocyte death in the failing human heart is gender dependent. Circ Res. 1999; 85: 856–866.
76. Olivetti G, Abbi R, Quaini F, Kajstura J, Cheng W, Nitahara JA, Quaini E, DiLoreto C, Beltrami CA, Krajewski S, Reed JC, Anversa P. Apoptosis in the failing human heart. N Engl J Med. 1997; 336: 1131–1141.
77. Anversa P. Myocyte death in the pathological heart. Circ Res. 2000; 86: 121–124.
78. Anversa P, Leri A, Beltrami CA, Guerra S, Kajstura J. Myocyte death and growth in the failing heart. Lab Invest. 1998; 78: 767–786.[Medline] [Order article via Infotrieve]
79. Nakamura T, Schneider MD. The way to a human’s heart is through the stomach: visceral endoderm-like cells drive human embryonic stem cells to a cardiac fate. Circulation. 2003; 107: 2638–2639.
80. Urbich C, Dimmeler S. Endothelial progenitor cells: characterization and role in vascular biology. Circ Res. 2004; 95: 343–353.
81. Oh H, Taffet GE, Youker KA, Entman ML, Overbeek PA, Michael LH, Schneider MD. Telomerase reverse transcriptase promotes cardiac muscle cell proliferation, hypertrophy, and survival. Proc Natl Acad Sci U S A. 2001; 98: 10308–10313.
82. Mori A, Hashino S, Kobayashi S, Tanaka J, Yamamoto Y, Asaka M, Imamura M. Avascular necrosis in the femoral head secondary to bone marrow infarction in a patient with graft-versus-host disease after unrelated bone marrow transplantation. Ann Hematol. 2001; 80: 238–242.[CrossRef][Medline] [Order article via Infotrieve]
83. Narayan S, Ezughah F, Standen GR, Pawade J, Kennedy CT. Idiopathic hypereosinophilic syndrome associated with cutaneous infarction and deep venous thrombosis. Br J Dermatol. 2003; 148: 817–820.[CrossRef][Medline] [Order article via Infotrieve]
84. Francque S, Condat B, Asselah T, Vilgrain V, Durand F, Moreau R, Valla D. Multifactorial aetiology of hepatic infarction: a case report with literature review. Eur J Gastroenterol Hepatol. 2004; 16: 411–415.[CrossRef][Medline] [Order article via Infotrieve]
85. Leong FT, Freeman LJ. Acute renal infarction. J R Soc Med. 2005; 98: 121–122.
86. Beltrami CA, Finato N. Rocco M, Feruglio GA, Puricelli C, Cigola E, Quaini F, Sonnenblick EH, Olivetti G, Anversa P. Structural basis of end-stage failure in ischemic cardiomyopathy in humans. Circulation. 1994; 89: 151–163.
87. Baerlocher GM, Roth A, Lansdorp PM. Telomeres in hematopoietic stem cells. Ann N Y Acad Sci. 2003; 996: 44–48.[CrossRef][Medline] [Order article via Infotrieve]
88. Samper E, Fernandez P, Martin-Rivera L, Bernad A, Blasco MA, Aracil M. Long-term repopulating ability of telomerase-deficient murine hematopoietic stem cells. Blood. 2002; 99: 2767–2775.
89. Flores I, Cayula Blasco MA. Effects of telomerase and telomere length on epidermal stem cell behavior. Science. 2005; 309: 1253–1256.
90. Mattern KA, Swiggers SJ, Nigg AL, Lowenberg B, Houtsmuller AB, Zijlmans JA. Dynamics of protein binding to telomeres in living cells: implications for telomere structure and function. Mol Cell Biol. 2004; 24: 5587–5594.
91. Ezoe S, Matsumura I, Satoh Y, Tanaka H, Kanakura Y. Cell cycle regulation in hematopoietic stem/progenitor cells. Cell Cycle. 2004; 3: 314–318.[Medline] [Order article via Infotrieve]
92. Campisi J. Senescent cells, tumor suppression, and organismal aging: good citizens, bad neighbors. Cell. 2005; 120: 513–522.[CrossRef][Medline] [Order article via Infotrieve]
93. Maggioni AP, Maseri A, Fresco C, Franzosi MG, Mauri F, Santoro E, Tognoni G. Age-related increase in mortality among patients with first myocardial infarctions treated with thrombolysis; the Investigators of the Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto Miocardico (GISSI-2). N Engl J Med. 1993; 329: 1442–1448.
94. Morrison SJ, Uchida N, Weissman IL. The biology of hematopoietic stem cells. Annu Rev Cell Dev Biol. 1995; 11: 35–71.[CrossRef][Medline] [Order article via Infotrieve]
95. Rossi DJ, Bryder D, Zahn JM, Alhenius H, Sonu R, Wagers AJ, Weissman Il. Cell intrinsic alterations underlie hematopoietic stem cell aging. Proc Natl Acad Sci U S A. 2005; 102: 9194–9199.
96. Anversa P, Olivetti G. Cellular basis of physiological and pathological myocardial growth. In: Page E, Fozzard HA, Solaro RJ, eds. Handbook of Physiology, Section 2: The Cardiovascular System: The Heart, Volume 1. New York, NY: Oxford University Press; 2002: 75–144.
97. Bagby GC, Lipton JM, Sloand EM, Schiffer CA. Marrow failure. Hematology. 2004; 1: 318–336.[CrossRef]
98. Chen J. Animal models for acquired bone marrow failure syndromes. Clin Med Res. 2005; 3: 102–108.
This article has been cited by other articles:
 |
|
 |
|
  J. Ferreira-Martins, C. Rondon-Clavo, D. Tugal, J. A. Korn, R. Rizzi, M. E. Padin-Iruegas, S. Ottolenghi, A. De Angelis, K. Urbanek, N. Ide-Iwata, et al. Spontaneous Calcium Oscillations Regulate Human Cardiac Progenitor Cell Growth Circ. Res., October 9, 2009; 105(8): 764 - 774. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. Fischer-Rasokat, B. Assmus, F. H. Seeger, J. Honold, D. Leistner, S. Fichtlscherer, V. Schachinger, T. Tonn, H. Martin, S. Dimmeler, et al. A Pilot Trial to Assess Potential Effects of Selective Intracoronary Bone Marrow-Derived Progenitor Cell Infusion in Patients With Nonischemic Dilated Cardiomyopathy: Final 1-Year Results of the Transplantation of Progenitor Cells and Functional Regeneration Enhancement Pilot Trial in Patients With Nonischemic Dilated Cardiomyopathy Circ Heart Fail, September 1, 2009; 2(5): 417 - 423. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Kania, P. Blyszczuk, S. Stein, A. Valaperti, D. Germano, S. Dirnhofer, L. Hunziker, C. M. Matter, and U. Eriksson Heart-Infiltrating Prominin-1+/CD133+ Progenitor Cells Represent the Cellular Source of Transforming Growth Factor {beta}-Mediated Cardiac Fibrosis in Experimental Autoimmune Myocarditis Circ. Res., August 28, 2009; 105(5): 462 - 470. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Cesselli, A. P. Beltrami, S. Rigo, N. Bergamin, F. D'Aurizio, R. Verardo, S. Piazza, E. Klaric, R. Fanin, B. Toffoletto, et al. Multipotent Progenitor Cells Are Present in Human Peripheral Blood Circ. Res., May 22, 2009; 104(10): 1225 - 1234. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Herbots, J. D'hooge, E. Eroglu, D. Thijs, J. Ganame, P. Claus, C. Dubois, K. Theunissen, J. Bogaert, J. Dens, et al. Improved regional function after autologous bone marrow-derived stem cell transfer in patients with acute myocardial infarction: a randomized, double-blind strain rate imaging study Eur. Heart J., March 2, 2009; 30(6): 662 - 670. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. J. Bogaard, K. Abe, A. Vonk Noordegraaf, and N. F. Voelkel The Right Ventricle Under Pressure: Cellular and Molecular Mechanisms of Right-Heart Failure in Pulmonary Hypertension Chest, March 1, 2009; 135(3): 794 - 804. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. L Kao, W. Browder, and C. Li Cellular Cardiomyoplasty: What Have We Learned? Asian Cardiovasc Thorac Ann, January 1, 2009; 17(1): 89 - 101. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. E. Schultze, R. J. Konrad, K. M. Credille, Q. A. Lu, and J. Todd Ultrasensitive Cross-species Measurement of Cardiac Troponin-I Using the Erenna Immunoassay System Toxicol Pathol, October 1, 2008; 36(6): 777 - 782. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Qiu, H. Dai, K. Jain, R. Shah, C. Hong, J. Pain, B. Tian, D. E. Vatner, S. F. Vatner, and C. Depre Characterization of a Novel Cardiac Isoform of the Cell Cycle-related Kinase That Is Regulated during Heart Failure J. Biol. Chem., August 8, 2008; 283(32): 22157 - 22165. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Rupp, M. Koyanagi, M. Iwasaki, J. Bauer, S. von Gerlach, D. Schranz, A. M. Zeiher, and S. Dimmeler Characterization of long-term endogenous cardiac repair in children after heart transplantation Eur. Heart J., August 1, 2008; 29(15): 1867 - 1872. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. H. Schuleri, L. C. Amado, A. J. Boyle, M. Centola, A. P. Saliaris, M. R. Gutman, K. E. Hatzistergos, B. N. Oskouei, J. M. Zimmet, R. G. Young, et al. Early improvement in cardiac tissue perfusion due to mesenchymal stem cells Am J Physiol Heart Circ Physiol, May 1, 2008; 294(5): H2002 - H2011. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. Murphy and C. Steenbergen Mechanisms Underlying Acute Protection From Cardiac Ischemia-Reperfusion Injury Physiol Rev, April 1, 2008; 88(2): 581 - 609. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Scobioala, R. Klocke, M. Kuhlmann, W. Tian, L. Hasib, H. Milting, S. Koenig, M. Stelljes, A. El-Banayosy, G. Tenderich, et al. Up-regulation of nestin in the infarcted myocardium potentially indicates differentiation of resident cardiac stem cells into various lineages including cardiomyocytes FASEB J, April 1, 2008; 22(4): 1021 - 1031. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Li, N. Naqvi, E. Yahiro, K. Liu, P. C. Powell, W. E. Bradley, D. I.K. Martin, R. M. Graham, L. J. Dell'Italia, and A. Husain c-kit Is Required for Cardiomyocyte Terminal Differentiation Circ. Res., March 28, 2008; 102(6): 677 - 685. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Kaczmarczyk Is the clinical use of adult stem cells a realistic possibility for myocardial regeneration? Bioscience Horizons, March 1, 2008; 1(1): 67 - 74. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Kehat and L. Gepstein Electrophysiological Coupling of Transplanted Cardiomyocytes Circ. Res., August 31, 2007; 101(5): 433 - 435. [Full Text] [PDF]
|
|
|
|
|
|
M. Rota, T. Hosoda, A. De Angelis, M. L. Arcarese, G. Esposito, R. Rizzi, J. Tillmanns, D. Tugal, E. Musso, O. Rimoldi, et al. The Young Mouse Heart Is Composed of Myocytes Heterogeneous in Age and Function Circ. Res., August 17, 2007; 101(4): 387 - 399. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. G. Zenovich and D. A. Taylor CELL THERAPY IN KIDNEY DISEASE: CAUTIOUS OPTIMISM... BUT OPTIMISM NONETHELESS Perit. Dial. Int., June 1, 2007; 27(Supplement_2): S94 - S103. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. H. Cingolani Cardiac Hypertrophy and the Wnt/Frizzled Pathway Hypertension, March 1, 2007; 49(3): 427 - 428. [Full Text] [PDF]
|
|
|
|
 |
|
 P. Anversa, J. Kajstura, and A. Leri If I Can Stop One Heart From Breaking Circulation, February 20, 2007; 115(7): 829 - 832. [Full Text] [PDF]
|
|
|
|
 |
|
 N N Chattergoon, G D Giraud, and K L Thornburg Thyroid hormone inhibits proliferation of fetal cardiac myocytes in vitro J. Endocrinol., February 1, 2007; 192(2): R1 - R8. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. R. Gaudette and I. S. Cohen Cardiac Regeneration: Materials Can Improve the Passive Properties of Myocardium, but Cell Therapy Must Do More Circulation, December 12, 2006; 114(24): 2575 - 2577. [Full Text] [PDF]
|
|
|
|
|
|
X. Wang and J. Robbins Heart Failure and Protein Quality Control Circ. Res., December 8, 2006; 99(12): 1315 - 1328. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Yamabi, H. Lu, X. Dai, Y. Lu, G. Hannigan, and J. G. Coles Overexpression of integrin-linked kinase induces cardiac stem cell expansion J. Thorac. Cardiovasc. Surg., December 1, 2006; 132(6): 1272 - 1279. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Hilfiker-Kleiner, U. Landmesser, and H. Drexler Molecular Mechanisms in Heart Failure: Focus on Cardiac Hypertrophy, Inflammation, Angiogenesis, and Apoptosis J. Am. Coll. Cardiol., October 27, 2006; 48(9_Suppl_A): A56 - A66. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Messina and A. Giacomello Diabetic Cardiomyopathy: A "Cardiac Stem Cell Disease" Involving p66Shc, an Attractive Novel Molecular Target for Heart Failure Therapy Circ. Res., July 7, 2006; 99(1): 1 - 2. [Full Text] [PDF]
|
|
|
|
|
|
M. Rota, N. LeCapitaine, T. Hosoda, A. Boni, A. De Angelis, M. E. Padin-Iruegas, G. Esposito, S. Vitale, K. Urbanek, C. Casarsa, et al. Diabetes Promotes Cardiac Stem Cell Aging and Heart Failure, Which Are Prevented by Deletion of the p66shc Gene Circ. Res., July 7, 2006; 99(1): 42 - 52. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Minerva BMJ, April 1, 2006; 332(7544): 802 - 802. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||