Biomedical subjects

Konrad Urbanek

Publications and source records attributed to Konrad Urbanek.

17 recordsLinked to original sources

PubMed2006

Concise review: stem cells, myocardial regeneration, and methodological artifacts.

This review discusses the current controversy about the role that endogenous and exogenous progenitor cells have in cardiac homeostasis and myocardial regeneration following injury. Although great enthusiasm was created by the possibility of reconstituting the damaged heart, the opponents of this new concept of cardiac biology have interpreted most of the findings supporting this possibility as the product of technical artifacts. This article challenges this established, static view of cardiac growth and favors the notion that the mammalian heart has the inherent ability to replace its cardiomyocytes through the activation of a pool of resident primitive cells or the administration of hematopoietic stem cells.

Artifacts↗

PubMed2006

Diabetes promotes cardiac stem cell aging and heart failure, which are prevented by deletion of the p66shc gene.

Diabetes leads to a decompensated myopathy, but the etiology of the cardiac disease is poorly understood. Oxidative stress is enhanced with diabetes and oxygen toxicity may alter cardiac progenitor cell (CPC) function resulting in defects in CPC growth and myocyte formation, which may favor premature myocardial aging and heart failure. We report that in a model of insulin-dependent diabetes mellitus, the generation of reactive oxygen species (ROS) leads to telomeric shortening, expression of the senescent associated proteins p53 and p16INK4a, and apoptosis of CPCs, impairing the growth reserve of the heart. However, ablation of the p66shc gene prevents these negative adaptations of the CPC compartment, interfering with the acquisition of the heart senescent phenotype and the development of heart failure with diabetes. ROS elicit 3 cellular reactions: low levels activate cell growth, intermediate quantities trigger cell apoptosis, and high amounts initiate cell necrosis. CPC replication predominates in diabetic p66shc-/-, whereas CPC apoptosis and myocyte apoptosis and necrosis prevail in diabetic wild type. Expansion of CPCs and developing myocytes preserves cardiac function in diabetic p66shc-/-, suggesting that intact CPCs can effectively counteract the impact of uncontrolled diabetes on the heart. The recognition that p66shc conditions the destiny of CPCs raises the possibility that diabetic cardiomyopathy is a stem cell disease in which abnormalities in CPCs define the life and death of the heart. Together, these data point to a genetic link between diabetes and ROS, on the one hand, and CPC survival and growth, on the other.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Stem cell niches in the adult mouse heart.

Cardiac stem cells (CSCs) have been identified in the adult heart, but the microenvironment that protects the slow-cycling, undifferentiated, and self-renewing CSCs remains to be determined. We report that the myocardium possesses interstitial structures with the architectural organization of stem cell niches that harbor long-term BrdU-retaining cells. The recognition of long-term label-retaining cells provides functional evidence of resident CSCs in the myocardium, indicating that the heart is an organ regulated by a stem cell compartment. Cardiac niches contain CSCs and lineage-committed cells, which are connected to supporting cells represented by myocytes and fibroblasts. Connexins and cadherins form gap and adherens junctions at the interface of CSCs-lineage-committed cells and supporting cells. The undifferentiated state of CSCs is coupled with the expression of alpha(4)-integrin, which colocalizes with the alpha(2)-chain of laminin and fibronectin. CSCs divide symmetrically and asymmetrically, but asymmetric division predominates, and the replicating CSC gives rise to one daughter CSC and one daughter committed cell. By this mechanism of growth kinetics, the pool of primitive CSCs is preserved, and a myocyte progeny is generated together with endothelial and smooth muscle cells. Thus, CSCs regulate myocyte turnover that is heterogeneous across the heart, faster at the apex and atria, and slower at the base-midregion of the ventricle.

Animals↗

PubMed2005

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↗

PubMed2005

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↗

PubMed2005

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↗

PubMed2005

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↗

PubMed2005

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↗

PubMed2005

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↗

PubMed2004

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↗

PubMed2004

Cardiac stem cell and myocyte aging, heart failure, and insulin-like growth factor-1 overexpression.

To determine whether cellular aging leads to a cardiomyopathy and heart failure, markers of cellular senescence, cell death, telomerase activity, telomere integrity, and cell regeneration were measured in myocytes of aging wild-type mice (WT). These parameters were similarly studied in insulin-like growth factor-1 (IGF-1) transgenic mice (TG) because IGF-1 promotes cell growth and survival and may delay cellular aging. Importantly, the consequences of aging on cardiac stem cell (CSC) growth and senescence were evaluated. Gene products implicated in growth arrest and senescence, such as p27Kip1, p53, p16INK4a, and p19ARF, were detected in myocytes of young WT mice, and their expression increased with age. IGF-1 attenuated the levels of these proteins at all ages. Telomerase activity decreased in aging WT myocytes but increased in TG, paralleling the changes in Akt phosphorylation. Reduction in nuclear phospho-Akt and telomerase resulted in telomere shortening and uncapping in WT myocytes. Senescence and death of CSCs increased with age in WT impairing the growth and turnover of cells in the heart. DNA damage and myocyte death exceeded cell formation in old WT, leading to a decreased number of myocytes and heart failure. This did not occur in TG in which CSC-mediated myocyte regeneration compensated for the extent of cell death preventing ventricular dysfunction. IGF-1 enhanced nuclear phospho-Akt and telomerase delaying cellular aging and death. The differential response of TG mice to chronological age may result from preservation of functional CSCs undergoing myocyte commitment. In conclusion, senescence of CSCs and myocytes conditions the development of an aging myopathy.

Aging↗

PubMed2003

Adult cardiac stem cells are multipotent and support myocardial regeneration.

The notion of the adult heart as terminally differentiated organ without self-renewal potential has been undermined by the existence of a subpopulation of replicating myocytes in normal and pathological states. The origin and significance of these cells has remained obscure for lack of a proper biological context. We report the existence of Lin(-) c-kit(POS) cells with the properties of cardiac stem cells. They are self-renewing, clonogenic, and multipotent, giving rise to myocytes, smooth muscle, and endothelial cells. When injected into an ischemic heart, these cells or their clonal progeny reconstitute well-differentiated myocardium, formed by blood-carrying new vessels and myocytes with the characteristics of young cells, encompassing approximately 70% of the ventricle. Thus, the adult heart, like the brain, is mainly composed of terminally differentiated cells, but is not a terminally differentiated organ because it contains stem cells supporting its regeneration. The existence of these cells opens new opportunities for myocardial repair.

Animals↗

PubMed2003

Senescence and death of primitive cells and myocytes lead to premature cardiac aging and heart failure.

Chronological myocardial aging is viewed as the inevitable effect of time on the functional reserve of the heart. Cardiac failure in elderly patients is commonly interpreted as an idiopathic or secondary myopathy superimposed on the old heart independently from the aging process. Thus, aged diseased hearts were studied to determine whether cell regeneration was disproportionate to the accumulation of old dying cells, leading to cardiac decompensation. Endomyocardial biopsies from 19 old patients with a dilated myopathy were compared with specimens from 7 individuals of similar age and normal ventricular function. Ten patients with idiopathic dilated cardiomyopathy were also analyzed to detect differences with aged diseased hearts. Senescent cells were identified by the expression of the cell cycle inhibitor p16INK4a and cell death by hairpin 1 and 2. Replication of primitive cells and myocytes was assessed by MCM5 labeling, myocyte mitotic index, and telomerase function. Aged diseased hearts had moderate hypertrophy and dilation, accumulation of p16INK4a positive primitive cells and myocytes, and no structural damage. Cell death markedly increased and occurred only in cells expressing p16INK4a that had significant telomeric shortening. Cell multiplication, mitotic index and telomerase increased but did not compensate for cell death or prevented telomeric shortening. Idiopathic dilated cardiomyopathy had severe hypertrophy and dilation, tissue injury, and minimal level of p16INK4a labeling. In conclusion, telomere erosion, cellular senescence, and death characterize aged diseased hearts and the development of cardiac failure in humans.

Aged↗

PubMed2003

Intense myocyte formation from cardiac stem cells in human cardiac hypertrophy.

It is generally believed that increase in adult contractile cardiac mass can be accomplished only by hypertrophy of existing myocytes. Documentation of myocardial regeneration in acute stress has challenged this dogma and led to the proposition that myocyte renewal is fundamental to cardiac homeostasis. Here we report that in human aortic stenosis, increased cardiac mass results from a combination of myocyte hypertrophy and hyperplasia. Intense new myocyte formation results from the differentiation of stem-like cells committed to the myocyte lineage. These cells express stem cell markers and telomerase. Their number increased >13-fold in aortic stenosis. The finding of cell clusters with stem cells making the transition to cardiogenic and myocyte precursors, as well as very primitive myocytes that turn into terminally differentiated myocytes, provides a link between cardiac stem cells and myocyte differentiation. Growth and differentiation of these primitive cells was markedly enhanced in hypertrophy, consistent with activation of a restricted number of stem cells that, through symmetrical cell division, generate asynchronously differentiating progeny. These clusters strongly support the existence of cardiac stem cells that amplify and commit to the myocyte lineage in response to increased workload. Their presence is consistent with the notion that myocyte hyperplasia significantly contributes to cardiac hypertrophy and accounts for the subpopulation of cycling myocytes.

Cardiomegaly↗

PubMed2002

bcl-2 overexpression promotes myocyte proliferation.

To determine the influence of Bcl-2 on the developmental biology of myocytes, we analyzed the population dynamics of this cell type in the heart of transgenic (TG) mice overexpressing Bcl-2 under the control of the alpha-myosin heavy chain promoter. TG mice and non-TG (wild type, WT) mice were studied at 24 days, 2 months, and 4 months after birth. Bcl-2 overexpression produced a significant increase in the percentage of cycling myocytes and their mitotic index. These effects were strictly connected to the expression of the transgene, as demonstrated in isolated myocytes. The formation of mitotic spindle and contractile ring was identified in replicating cells. These typical aspects of mitosis were complemented with the demonstration of karyokinesis and cytokinesis to provide structural evidence of cell division. Apoptosis was low at all ages and was not affected by Bcl-2. The higher cell replication rate in TG was conditioned by a decrease in the expression of the cell-cycle inhibitors, p21(WAF1) and p16(INK4a), and by an increase in Mdm2-p53 complexes. In comparison with WT, TG had 0.4 x 10(6), 0.74 x 10(6), and 1.2 x 10(6) more myocytes in the left ventricle at 24 days, 2 months, and 4 months, respectively. Binucleated myocytes were 12% and 25% larger in WT than in TG mice at 2 and 4 months of age. Taken together, these observations reveal a previously uncharacterized replication-enhancing function of Bcl-2 in myocytes in vivo in the absence of stressful conditions.

Animals↗

PubMed2002

Chimerism of the transplanted heart.

BACKGROUND: Cases in which a male patient receives a heart from a female donor provide an unusual opportunity to test whether primitive cells translocate from the recipient to the graft and whether cells with the phenotypic characteristics of those of the recipient ultimately reside in the donor heart. The Y chromosome can be used to detect migrated undifferentiated cells expressing stem-cell antigens and to discriminate between primitive cells derived from the recipient and those derived from the donor. METHODS: We examined samples from the atria of the recipient and the atria and ventricles of the graft by fluorescence in situ hybridization to determine whether Y chromosomes were present in eight hearts from female donors implanted into male patients. Primitive cells bearing Y chromosomes that expressed c-kit, MDR1, and Sca-1 were also investigated. RESULTS: Myocytes, coronary arterioles, and capillaries that had a Y chromosome made up 7 to 10 percent of those in the donor hearts and were highly proliferative. As compared with the ventricles of control hearts, the ventricles of the transplanted hearts had markedly increased numbers of cells that were positive for c-kit, MDR1, or Sca-1. The number of primitive cells was higher in the atria of the hosts and the atria of the donor hearts than in the ventricles of the donor hearts, and 12 to 16 percent of these cells contained a Y chromosome. Undifferentiated cells were negative for markers of bone marrow origin. Progenitor cells expressing MEF2, GATA-4, and nestin (which identify the cells as myocytes) and Flk1 (which identifies the cells as endothelial cells) were identified. CONCLUSIONS: Our results show a high level of cardiac chimerism caused by the migration of primitive cells from the recipient to the grafted heart. Putative stem cells and progenitor cells were identified in control myocardium and in increased numbers in transplanted hearts.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMedDate not supplied

The telomere-telomerase axis and the heart.

The preservation of myocyte number and cardiac mass throughout life is dependent on the balance between cell death and cell division. Rapidly emerging evidence indicates that new myocytes can be formed through the activation and differentiation of resident cardiac progenitor cells. The critical issue is the identification of mechanisms that define the aging of cardiac progenitor cells and, ultimately, their inability to replace dying myocytes. The most reliable marker of cellular senescence is the modification of the telomere-telomerase axis, together with the expression of the cell cycle inhibitors p16INK4a and p53. Cellular senescence is characterized by biochemical events that occur within the cell. In this regard, one of the most relevant processes is represented by repeated oxidative stress that may evolve into the activation of the cell death program or result in the development of a senescent phenotype. Thus, the modulation of telomerase activity and the control of telomeric length, together with the attenuation of the formation of reactive oxygen species, may represent important therapeutic tools in regenerative medicine and in prevention of aging and diabetic cardiomyopathies.

Animals↗