Endothelial progenitor cells: neovascularization or more?
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Animals↗
Biomedical subjects
Annarosa Leri
Publications and source records attributed to Annarosa Leri.
Nuclear targeting of Akt enhances ventricular function and myocyte contractility.
Cytoplasmic overexpression of Akt in the heart results in a myopathy characterized by organ and myocyte hypertrophy. Conversely, nuclear-targeted Akt does not lead to cardiac hypertrophy, but the cellular basis of this distinct heart phenotype remains to be determined. Similarly, whether nuclear-targeted Akt affects ventricular performance and mechanics, calcium metabolism, and electrical properties of myocytes is unknown. Moreover, whether the expression and state of phosphorylation of regulatory proteins implicated in calcium cycling and myocyte contractility are altered in nuclear-targeted Akt has not been established. We report that nuclear overexpression of Akt does not modify cardiac size and shape but results in an increased number of cardiomyocytes, which are smaller in volume. Additionally, the heart possesses enhanced systolic and diastolic function, which is paralleled by increased myocyte performance. Myocyte shortening and velocity of shortening and relengthening are increased in transgenic mice and are coupled with a more efficient reuptake of calcium by the sarcoplasmic reticulum (SR). This process increases calcium loading of the SR during relengthening. The enhanced SR function appears to be mediated by an increase in SR Ca2+-ATPase2a activity sustained by a higher degree of phosphorylation of phospholamban. This posttranslational modification was associated with an increase in phospho-protein kinase A and a decrease in protein phosphatase-1. Together, these observations provide a plausible biochemical mechanism for the potentiation of myocyte and ventricular function in Akt transgenic mice. Therefore, nuclear-targeted Akt in myocytes may have important implications for the diseased heart.
Actin Cytoskeleton↗
Cardiac stem cells possess growth factor-receptor systems that after activation regenerate the infarcted myocardium, improving ventricular function and long-term survival.
Cardiac stem cells and early committed cells (CSCs-ECCs) express c-Met and insulin-like growth factor-1 (IGF-1) receptors and synthesize and secrete the corresponding ligands, hepatocyte growth factor (HGF) and IGF-1. HGF mobilizes CSCs-ECCs and IGF-1 promotes their survival and proliferation. Therefore, HGF and IGF-1 were injected in the hearts of infarcted mice to favor, respectively, the translocation of CSCs-ECCs from the surrounding myocardium to the dead tissue and the viability and growth of these cells within the damaged area. To facilitate migration and homing of CSCs-ECCs to the infarct, a growth factor gradient was introduced between the site of storage of primitive cells in the atria and the region bordering the infarct. The newly-formed myocardium contained arterioles, capillaries, and functionally competent myocytes that with time increased in size, improving ventricular performance at healing and long thereafter. The volume of regenerated myocytes was 2200 microm3 at 16 days after treatment and reached 5100 microm3 at 4 months. In this interval, nearly 20% of myocytes reached the adult phenotype, varying in size from 10,000 to 20,000 microm3. Moreover, there were 43+/-13 arterioles and 155+/-48 capillaries/mm2 myocardium at 16 days, and 31+/-6 arterioles and 390+/-56 capillaries at 4 months. Myocardial regeneration induced increased survival and rescued animals with infarcts that were up to 86% of the ventricle, which are commonly fatal. In conclusion, the heart has an endogenous reserve of CSCs-ECCs that can be activated to reconstitute dead myocardium and recover cardiac function.
Animals↗
Endothelial progenitor cells: unexpected disclosures.
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Antigens, CD34↗
PI3K rescues the detrimental effects of chronic Akt activation in the heart during ischemia/reperfusion injury.
Acute activation of the serine-threonine kinase Akt is cardioprotective and reduces both infarction and dysfunction after ischemia/reperfusion injury (IRI). However, less is known about the chronic effects of Akt activation in the heart, and, paradoxically, Akt is activated in samples from patients with chronic heart failure. We generated Tg mice with cardiac-specific expression of either activated (myristoylated [myr]) or dominant-negative (dn) Akt and assessed their response to IRI in an ex vivo model. While dn-Akt hearts demonstrated a moderate reduction in functional recovery after IRI, no function was restored in any of the myr-Akt-Tg hearts. Moreover, infarcts were dramatically larger in myr-Akt-Tg hearts. Biochemical analyses demonstrated that chronic Akt activation induces feedback inhibition of PI3K activity through both proteasome-dependent degradation of insulin receptor substrate-1 (IRS-1) and inhibition of transcription of IRS-1 as well as that of IRS-2. To test the functional significance of these signaling changes, we performed in vivo cardiac gene transfer with constitutively active PI3K in myr-Akt-Tg mice. Restoration of PI3K rescued function and reduced injury after IRI. These data demonstrate that PI3K-dependent but Akt-independent effectors are required for full cardioprotection and suggest a mechanism by which chronic Akt activation can become maladaptive.
Animals↗
Stem cells in the dog heart are self-renewing, clonogenic, and multipotent and regenerate infarcted myocardium, improving cardiac function.
The purpose of this study was to determine whether the heart in large mammals contains cardiac progenitor cells that regulate organ homeostasis and regenerate dead myocardium after infarction. We report that the dog heart possesses a cardiac stem cell pool characterized by undifferentiated cells that are self-renewing, clonogenic, and multipotent. These clonogenic cells and early committed progeny possess a hepatocyte growth factor (HGF)-c-Met and an insulin-like growth factor 1 (IGF-1)-IGF-1 receptor system that can be activated to induce their migration, proliferation, and survival. Therefore, myocardial infarction was induced in chronically instrumented dogs implanted with sonomicrometric crystals in the region of the left ventricular wall supplied by the occluded left anterior descending coronary artery. After infarction, HGF and IGF-1 were injected intramyocardially to stimulate resident cardiac progenitor cells. This intervention led to the formation of myocytes and coronary vessels within the infarct. Newly generated myocytes expressed nuclear and cytoplasmic proteins specific of cardiomyocytes: MEF2C was detected in the nucleus, whereas alpha-sarcomeric actin, cardiac myosin heavy chain, troponin I, and alpha-actinin were identified in the cytoplasm. Connexin 43 and N-cadherin were also present. Myocardial reconstitution resulted in a marked recovery of contractile performance of the infarcted heart. In conclusion, the activation of resident primitive cells in the damaged dog heart can promote a significant restoration of dead tissue, which is paralleled by a progressive improvement in cardiac function. These results suggest that strategies capable of activating the growth reserve of the myocardium may be important in cardiac repair after ischemic injury.
Animals↗
Myocardial regeneration by activation of multipotent cardiac stem cells in ischemic heart failure.
In this study, we tested whether the human heart possesses a cardiac stem cell (CSC) pool that promotes regeneration after infarction. For this purpose, CSC growth and senescence were measured in 20 hearts with acute infarcts, 20 hearts with end-stage postinfarction cardiomyopathy, and 12 control hearts. CSC number increased markedly in acute and, to a lesser extent, in chronic infarcts. CSC growth correlated with the increase in telomerase-competent dividing CSCs from 1.5% in controls to 28% in acute infarcts and 14% in chronic infarcts. The CSC mitotic index increased 29-fold in acute and 14-fold in chronic infarcts. CSCs committed to the myocyte, smooth muscle, and endothelial cell lineages increased approximately 85-fold in acute infarcts and approximately 25-fold in chronic infarcts. However, p16(INK4a)-p53-positive senescent CSCs also increased and were 10%, 18%, and 40% in controls, acute infarcts, and chronic infarcts, respectively. Old CSCs had short telomeres and apoptosis involved 0.3%, 3.8%, and 9.6% of CSCs in controls, acute infarcts, and chronic infarcts, respectively. These variables reduced the number of functionally competent CSCs from approximately 26,000/cm3 of viable myocardium in acute to approximately 7,000/cm3 in chronic infarcts, respectively. In seven acute infarcts, foci of spontaneous myocardial regeneration that did not involve cell fusion were identified. In conclusion, the human heart possesses a CSC compartment, and CSC activation occurs in response to ischemic injury. The loss of functionally competent CSCs in chronic ischemic cardiomyopathy may underlie the progressive functional deterioration and the onset of terminal failure.
Apoptosis↗
Regenerating the myocardium: a reality today.
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Animals↗
Cardiac stem cells delivered intravascularly traverse the vessel barrier, regenerate infarcted myocardium, and improve cardiac function.
The ability of cardiac stem cells (CSCs) to promote myocardial repair under clinically relevant conditions (i.e., when delivered intravascularly after reperfusion) is unknown. Thus, rats were subjected to a 90-min coronary occlusion; at 4 h after reperfusion, CSCs were delivered to the coronary arteries via a catheter positioned into the aortic root. Echocardiographic analysis showed that injection of CSCs attenuated the increase in left ventricular (LV) end-diastolic dimensions and impairment in LV systolic performance at 5 weeks after myocardial infarction. Pathologic analysis showed that treated hearts exhibited a smaller increase in LV chamber diameter and volume and a higher wall thickness-to-chamber radius ratio and LV mass-to-chamber volume ratio. CSCs induced myocardial regeneration, decreasing infarct size by 29%. A diploid DNA content and only two chromosomes 12 were found in new cardiomyocytes, indicating that cell fusion did not contribute to tissue reconstitution. In conclusion, intravascular injection of CSCs after reperfusion limits infarct size, attenuates LV remodeling, and ameliorates LV function. This study demonstrates that CSCs are effective when delivered in a clinically relevant manner, a clear prerequisite for clinical translation, and that these beneficial effects are independent of cell fusion. The results establish CSCs as candidates for cardiac regeneration and support an approach in which the heart's own stem cells could be collected, expanded, and stored for subsequent therapeutic repair.
Animals↗
Myocardial aging--a stem cell problem.
This review questions the old paradigm that describes the heart as a post-mitotic organ and introduces the notion of the heart as a self-renewing organ regulated by a compartment of multipotent cardiac stem cells (CSCs) capable of regenerating myocytes and coronary vessels throughout life. Because of this dramatic change in cardiac biology, the objective is to provide an alternative perspective of the aging process of the heart and stimulate research in an area that pertains to all of us without exception. The recent explosion of the field of stem cell biology, with the recognition that the possibility exists for extrinsic and intrinsic regeneration of myocytes and coronary vessels, necessitates reevaluation of cardiac homeostasis and myocardial aging. From birth to senescence, the mammalian heart is composed of non-dividing and dividing cells. Loss of telomeric DNA is minimal in fetal and neonatal myocardium but rather significant in the senescent heart. Aging affects the growth and differentiation potential of CSCs interfering not only with their ability to sustain physiological cell turnover but also with their capacity to adapt to increases in pressure and volume loads. The recognition of factors enhancing the activation of the CSC pool, their mobilization, and translocation, however, suggests that the detrimental effects of aging on the heart might be prevented or reversed by local stimulation of CSCs or the intramyocardial delivery of CSCs following their expansion and rejuvenation in vitro. CSC therapy may become, perhaps, a novel strategy for the devastating problem of heart failure in the old population.
Aging↗
Identity deception: not a crime for a stem cell.
Stem cell transdifferentiation in the adult organism is the most common and questioned mechanism of growth and repair. Recent data suggest that adult stem cells are capable of generating mature cells beyond their own tissue boundaries, a process called developmental plasticity. To date, the most versatile cell discovered is the bone marrow progenitor cell.
Animals↗
Cardiac stem cells and mechanisms of myocardial regeneration.
This review discusses current understanding of the role that endogenous and exogenous progenitor cells may have in the treatment of the diseased heart. In the last several years, a major effort has been made in an attempt to identify immature cells capable of differentiating into cell lineages different from the organ of origin to be employed for the regeneration of the damaged heart. Embryonic stem cells (ESCs) and bone marrow-derived cells (BMCs) have been extensively studied and characterized, and dramatic advances have been made in the clinical application of BMCs in heart failure of ischemic and nonischemic origin. However, a controversy exists concerning the ability of BMCs to acquire cardiac cell lineages and reconstitute the myocardium lost after infarction. The recognition that the adult heart possesses a stem cell compartment that can regenerate myocytes and coronary vessels has raised the unique possibility to rebuild dead myocardium after infarction, to repopulate the hypertrophic decompensated heart with new better functioning myocytes and vascular structures, and, perhaps, to reverse ventricular dilation and wall thinning. Cardiac stem cells may become the most important cell for cardiac repair.
Animals↗
Cardiac stem cells and myocardial regeneration.
Until recently, the accepted paradigm considered the adult mammalian heart a post-mitotic organ without intrinsic regenerative capacity where neither myocyte death nor new myocyte formation played any role in its homeostasis and could be safely ignored. We have recently identified in the adult mammalian myocardium a small cell population expressing surface antigens commonly associated with a variety of stem cells. These cells have the behaviour and potential of bonafide cardiac stem cells (CSCs): they are clonogenic, self-renewing and multipotent. Their presence has identified myocyte death and myocyte renewal as the two sides of the proverbial coin of cardiac homeostasis. Myocyte renewal depends on the differentiation of the CSCs into immature myocytes that divide two to four times before becoming terminally differentiated. Both in vivo and in vitro the progeny of a single CSC can generate the three major cell types of the myocardium: myocytes, smooth muscle and endothelial vascular cells. More interestingly, when directly injected or activated with growth factors in the post-ischaemic myocardium, these cells are able to reconstitute a functional ventricular wall. Thus, although in the adult heart most cardiac myocytes are permanently withdrawn from the cell cycle, the heart has an intrinsic regenerative potential and it is not a terminally differentiated organ.
Animals↗
Bone marrow cells differentiate in cardiac cell lineages after infarction independently of cell fusion.
Recent studies in mice have challenged the ability of bone marrow cells (BMCs) to differentiate into myocytes and coronary vessels. The claim has also been made that BMCs acquire a cell phenotype different from the blood lineages only by fusing with resident cells. Technical problems exist in the induction of myocardial infarction and the successful injection of BMCs in the mouse heart. Similarly, the accurate analysis of the cell populations implicated in the regeneration of the dead tissue is complex and these factors together may account for the negative findings. In this study, we have implemented a simple protocol that can easily be reproduced and have reevaluated whether injection of BMCs restores the infarcted myocardium in mice and whether cell fusion is involved in tissue reconstitution. For this purpose, c-kit-positive BMCs were obtained from male transgenic mice expressing enhanced green fluorescence protein (EGFP). EGFP and the Y-chromosome were used as markers of the progeny of the transplanted cells in the recipient heart. By this approach, we have demonstrated that BMCs, when properly administrated in the infarcted heart, efficiently differentiate into myocytes and coronary vessels with no detectable differentiation into hemopoietic lineages. However, BMCs have no apparent paracrine effect on the growth behavior of the surviving myocardium. Within the infarct, in 10 days, nearly 4.5 million biochemically and morphologically differentiated myocytes together with coronary arterioles and capillary structures were generated independently of cell fusion. In conclusion, BMCs adopt the cardiac cell lineages and have an important therapeutic impact on ischemic heart failure.
Animals↗
Circulating progenitor cells: search for an identity.
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Adult↗
Nuclear targeting of Akt enhances kinase activity and survival of cardiomyocytes.
Heart failure is associated with death of cardiomyocytes leading to loss of contractility. Previous studies using membrane-targeted Akt (myristolated-Akt), an enzyme involved in antiapoptotic signaling, showed inhibition of cell death and prevention of pathogenesis induced by cardiomyopathic stimuli. However, recent studies by our group have found accumulation of activated Akt in the nucleus, suggesting that biologically relevant target(s) of Akt activity may be located there. To test this hypothesis, a targeted Akt construct was created to determine the antiapoptotic action of nuclear Akt accumulation. Nuclear localization of the adenovirally encoded Akt construct was confirmed by confocal microscopy. Cardiomyocytes expressing nuclear-targeted Akt showed no evidence of morphological remodeling such as altered myofibril density or hypertrophy. Nuclear-targeted Akt significantly elevated levels of phospho-Akt and kinase activity and inhibited apoptosis as effectively as myristolated-Akt in hypoxia-induced cell death. Transgenic overexpression of nuclear-targeted Akt did not result in hypertrophic remodeling, altered cardiomyocyte DNA content or nucleation, or enhanced phosphorylation of typical cytoplasmic Akt substrates, yet transgenic hearts were protected from ischemia-reperfusion injury. Gene array analyses demonstrated changes in the transcriptional profile of Akt/nuc hearts compared with nontransgenic controls distinct from prior characterizations of Akt expression in transgenic hearts. Collectively, these experiments show that targeting of Akt to the nucleus mediates inhibition of apoptosis without hypertrophic remodeling, opening new possibilities for therapeutic applications of nuclear-targeted Akt to inhibit cell death associated with heart disease.
Active Transport, Cell Nucleus↗
Regeneration of the infarcted heart with stem cells derived by nuclear transplantation.
Nuclear transfer techniques have been proposed as a strategy for generating an unlimited supply of rejuvenated and histocompatible stem cells for the treatment of cardiac diseases. For this purpose, c-kit-positive fetal liver stem cells obtained from cloned embryos were injected in the border zone of infarcted mice to induce tissue reconstitution. Cloned embryos were derived from somatic cell fusion between nuclei of cultured LacZ-positive fibroblasts and enucleated oocytes of a different mouse strain. We report that regenerating myocardium replaced 38% of the scar at 1 month. The rebuilt tissue expressed LacZ and was composed of myocytes and vessels connected with the coronary circulation. Myocytes were functionally competent and expressed contractile proteins, desmin, connexin43, and N-cadherin. These structural characteristics indicated that the new myocytes were electrically and mechanically coupled. Similarly, the formed coronary arterioles and capillary structures contained blood and contributed, therefore, to tissue oxygenation. Cardiac replacement resulted in an improvement of ventricular hemodynamics and in a reduction of diastolic wall stress. These beneficial effects were obtained by stem cell transdifferentiation and commitment to the cardiac cell lineages. Myocardial growth was independent from fusion of the injected stem cells with preexisting partner cells. In conclusion, c-kit-positive stem cells derived by nuclear transfer cloning restore infarcted myocardium. Although problems currently plague nuclear transplantation, including the potential for epigenetic and imprinting abnormalities, stem cells derived from cloned embryos are sufficiently normal to repair damaged tissue in vivo. Importantly, the magnitude of myocardial regeneration obtained in this study is significantly superior to that achieved with adult bone marrow cells.
Animals↗