The regenerative potential of the human heart.
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Animals↗
Biomedical subjects
P Anversa
Publications and source records attributed to P Anversa.
Transgenic overexpression of insulin-like growth factor I prevents streptozotocin-induced cardiac contractile dysfunction and beta-adrenergic response in ventricular myocytes.
Diabetic cardiomyopathy is characterized by cardiac dysfunction and altered level/function of insulin-like growth factor I (IGF-I). Both endogenous and exogenous IGF-I have been shown to effectively alleviate diabetes-induced cardiac dysfunction and oxidative stress. This study was designed to examine the effect of cardiac overexpression of IGF-I on streptozotocin (STZ)-induced cardiac contractile dysfunction in mouse myocytes. Both IGF-I heterozygous transgenic mice and their wild-type FVB littermates were made diabetic with a single injection of STZ (200 mg/kg, i.p.) and maintained for 2 weeks. The following mechanical indices were evaluated in ventricular myocytes: peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening/relengthening (+/- dL/dt). Intracellular Ca2+ was evaluated as resting and peak intracellular Ca2+ levels, Ca2+-induced Ca2+ release and intracellular Ca2+ decay rate (tau). STZ led to hyperglycemia in FVB and IGF-I mice. STZ treatment prolonged TPS and TR90, reduced Ca2+-induced Ca2+ release, increased resting intracellular Ca2+ levels and slowed tau associated with normal PS and +/- dL/dt. All of which, except the elevated resting intracellular Ca2+, were prevented by the IGF-I transgene. In addition, myocytes from STZ-treated FVB mice displayed an attenuated contractile response to the beta-adrenergic agonist isoproterenol, which was restored by the IGF-I transgene. Contractile response to the alpha-adrenergic agonist phenylephrine and angiotensin II was not affected by either STZ treatment or IGF-I. These results validate the beneficial role of IGF-I in diabetic cardiomyopathy, possibly due to an improved beta-adrenergic response.
Adrenergic alpha-Agonists↗
Mobilized bone marrow cells repair the infarcted heart, improving function and survival.
Attempts to repair myocardial infarcts by transplanting cardiomyocytes or skeletal myoblasts have failed to reconstitute healthy myocardium and coronary vessels integrated structurally and functionally with the remaining viable portion of the ventricular wall. The recently discovered growth and transdifferentiation potential of primitive bone marrow cells (BMC) prompted us, in an earlier study, to inject in the border zone of acute infarcts Lin(-) c-kit(POS) BMC from syngeneic animals. These BMC differentiated into myocytes and vascular structures, ameliorating the function of the infarcted heart. Two critical determinants seem to be required for the transdifferentiation of primitive BMC: tissue damage and a high level of pluripotent cells. On this basis, we hypothesized here that BMC, mobilized by stem cell factor and granulocyte-colony stimulating factor, would home to the infarcted region, replicate, differentiate, and ultimately promote myocardial repair. We report that, in the presence of an acute myocardial infarct, cytokine-mediated translocation of BMC resulted in a significant degree of tissue regeneration 27 days later. Cytokine-induced cardiac repair decreased mortality by 68%, infarct size by 40%, cavitary dilation by 26%, and diastolic stress by 70%. Ejection fraction progressively increased and hemodynamics significantly improved as a consequence of the formation of 15 x 10(6) new myocytes with arterioles and capillaries connected with the circulation of the unaffected ventricle. In conclusion, mobilization of primitive BMC by cytokines might offer a noninvasive therapeutic strategy for the regeneration of the myocardium lost as a result of ischemic heart disease and, perhaps, other forms of cardiac pathology.
Animals↗
Oxidative stress-mediated cardiac cell death is a major determinant of ventricular dysfunction and failure in dog dilated cardiomyopathy.
Cell death has been questioned as a mechanism of ventricular failure. In this report, we tested the hypothesis that apoptotic death of myocytes, endothelial cells, and fibroblasts is implicated in the development of the dilated myopathy induced by ventricular pacing. Accumulation of reactive oxygen products such as nitrotyrosine, potentiation of the oxidative stress response by p66(shc) expression, formation of p53 fragments, release of cytochrome c, and caspase activation were examined to establish whether these events were coupled with apoptotic cell death in the paced dog heart. Myocyte, endothelial cell, and fibroblast apoptosis was detected before indices of severe impairment of cardiac function became apparent. Cell death increased with the duration of pacing, and myocyte death exceeded endothelial cell and fibroblast death throughout. Nitrotyrosine formation and p66(shc) levels progressively increased with pacing and were associated with cell apoptosis. Similarly, p50 (DeltaN) fragments augmented paralleling the degree of cell death in the failing heart. Moreover, cytochrome c release and activation of caspase-9 and -3 increased from 1 to 4 weeks of pacing. In conclusion, cardiac cell death precedes ventricular decompensation and correlates with the time-dependent deterioration of function in this model. Oxidative stress may be critical for activation of apoptosis in the overloaded heart.
Adaptor Proteins, Signal Transducing↗
Telomerase expression and activity are coupled with myocyte proliferation and preservation of telomeric length in the failing heart.
The role and even the existence of myocyte proliferation in the adult heart remain controversial. Documentation of cell cycle regulators, DNA synthesis, and mitotic images has not modified the view that myocardial growth can only occur from hypertrophy of an irreplaceable population of differentiated myocytes. To improve understanding the biology of the heart and obtain supportive evidence of myocyte replication, three indices of cell proliferation were analyzed in dogs affected by a progressive deterioration of cardiac performance and dilated cardiomyopathy. The magnitude of cycling myocytes was evaluated by the expression of Ki67 in nuclei. Ki67 labeling of left ventricular myocytes increased 5-fold, 12-fold, and 17-fold with the onset of moderate and severe ventricular dysfunction and overt failure, respectively. Telomerase activity in vivo is present only in multiplying cells; this enzyme increased 2.4-fold and 3.1-fold in the decompensated heart, preserving telomeric length in myocytes. The contribution of cycling myocytes to telomerase activity was determined by the colocalization of Ki67 and telomerase in myocyte nuclei. More than 50% of Ki67-positive cells expressed telomerase in the overloaded myocardium, suggesting that these myocytes were the morphological counterpart of the biochemical assay of enzyme activity. Moreover, we report that 20--30% of canine myocytes were telomerase competent, and this value was not changed by cardiac failure. In conclusion, the enhanced expression of Ki67 and telomerase activity, in combination with Ki67-telomerase labeling of myocyte nuclei, support the notion that myocyte proliferation contributes to cardiac hypertrophy of the diseased heart.
Animals↗
Evidence that human cardiac myocytes divide after myocardial infarction.
BACKGROUND: The scarring of the heart that results from myocardial infarction has been interpreted as evidence that the heart is composed of myocytes that are unable to divide. However, recent observations have provided evidence of proliferation of myocytes in the adult heart. Therefore, we studied the extent of mitosis among myocytes after myocardial infarction in humans. METHODS: Samples from the border of the infarct and from areas of the myocardium distant from the infarct were obtained from 13 patients who had died 4 to 12 days after infarction. Ten normal hearts were used as controls. Myocytes that had entered the cell cycle in preparation for cell division were measured by labeling of the nuclear antigen Ki-67, which is associated with cell division. The fraction of myocyte nuclei that were undergoing mitosis was determined, and the mitotic index (the ratio of the number of nuclei undergoing mitosis to the number not undergoing mitosis) was calculated. The presence of mitotic spindles, contractile rings, karyokinesis, and cytokinesis was also recorded. RESULTS: In the infarcted hearts, Ki-67 expression was detected in 4 percent of myocyte nuclei in the regions adjacent to the infarcts and in 1 percent of those in regions distant from the infarcts. The reentry of myocytes into the cell cycle resulted in mitotic indexes of 0.08 percent and 0.03 percent, respectively, in the zones adjacent to and distant from the infarcts. Events characteristic of cell division--the formation of the mitotic spindles, the formation of contractile rings, karyokinesis, and cytokinesis--were identified; these features demonstrated that there was myocyte proliferation after myocardial infarction. CONCLUSIONS: Our results challenge the dogma that the adult heart is a postmitotic organ and indicate that the regeneration of myocytes may be a critical component of the increase in muscle mass of the myocardium.
Antibodies, Monoclonal↗
Myocardial Akt activation and gender: increased nuclear activity in females versus males.
Cardiovascular disease risk is higher in men than women, but the basis for this discrepancy remains controversial. Estrogenic stimulation of the myocardium or isolated cardiomyocytes has been purported to exert multiple beneficial effects associated with inhibition of maladaptive responses to pathogenic insults. This report describes a significant difference between the sexes in myocardial activation of Akt, a protein kinase that regulates a broad range of physiological responses including metabolism, gene transcription, and cell survival. We find that young women possess higher levels of nuclear-localized phospho-Akt(473) relative to comparably aged men or postmenopausal women. Both localization of phospho-Akt(473) in myocardial nuclei of sexually mature female mice versus males and Akt kinase activity in nuclear extracts of hearts from female mice versus males are elevated. Cytosolic localization of phospho-forkhead, a downstream nuclear target of Akt, is also increased in female relative to male mice, suggesting a potential mechanism for cardioprotective nuclear signaling resulting from Akt activation. Phospho-Akt(473) levels and localization at cardiac nuclei are similarly increased in transgenic mice with myocardium-specific expression of insulin-like growth factor I, a proven stimulus for Akt activation. Phospho-Akt(473) is also localized to the nucleus of cultured cardiomyocytes after exposure to 17beta-estradiol or genistein (a phytoestrogen in soy protein-based diets), and neonatal exposure of litters to genistein elevated nuclear phospho-Akt(473) localization. The activation of Akt in a gender-dependent manner may help explain differences observed in cardiovascular disease risk between the sexes and supports the potential beneficial effects of estrogenic stimulation.
Active Transport, Cell Nucleus↗
Bone marrow cells regenerate infarcted myocardium.
Myocardial infarction leads to loss of tissue and impairment of cardiac performance. The remaining myocytes are unable to reconstitute the necrotic tissue, and the post-infarcted heart deteriorates with time. Injury to a target organ is sensed by distant stem cells, which migrate to the site of damage and undergo alternate stem cell differentiation; these events promote structural and functional repair. This high degree of stem cell plasticity prompted us to test whether dead myocardium could be restored by transplanting bone marrow cells in infarcted mice. We sorted lineage-negative (Lin-) bone marrow cells from transgenic mice expressing enhanced green fluorescent protein by fluorescence-activated cell sorting on the basis of c-kit expression. Shortly after coronary ligation, Lin- c-kitPOS cells were injected in the contracting wall bordering the infarct. Here we report that newly formed myocardium occupied 68% of the infarcted portion of the ventricle 9 days after transplanting the bone marrow cells. The developing tissue comprised proliferating myocytes and vascular structures. Our studies indicate that locally delivered bone marrow cells can generate de novo myocardium, ameliorating the outcome of coronary artery disease.
Animals↗
Reperfusion-activated Akt kinase prevents apoptosis in transgenic mouse hearts overexpressing insulin-like growth factor-1.
Abstract -Hearts of wild-type and insulin-like growth factor-1 overexpressing (Igf-1(+/-)) transgenic mice were subjected to Langendorff perfusions and progressive periods of ischemia followed by reperfusion. Apoptosis was measured by DNA nucleosomal cleavage and a hairpin probe labeling assay to detect single-base overhang. Transgenic hearts subjected to 20 minutes of ischemia and 4 hours of reperfusion (I/R) sustained a rate of apoptosis of 1.8+/-0.3% compared with 4.6+/-1.1% for wild-type controls (n=4; P<0.03). Phosphorylation of the protein kinase Akt/protein kinase B was elevated 6.2-fold in transgenic hearts at baseline and increased another 4.4-fold within 10 minutes of reperfusion, remaining elevated for up to 2 hours. I/R activated Akt in wild-type hearts but to a lesser extent (1.6+/-0.3-fold). Pretreatment of transgenic hearts with wortmannin immediately before and during ischemia eliminated reperfusion-mediated activation of Akt and neutralized the resistance to apoptosis. The stress-activated kinase p38 was also activated during ischemia and reperfusion in both wild-type and transgenic hearts. Perfusion with the p38 inhibitor SB203580 (10 micromol/L) blocked both p38 activation and phosphorylation of Akt and differentially modulated apoptosis in wild-type and transgenic hearts. Pretreatment with SB203580 reduced apoptosis in wild-type hearts but increased apoptosis in transgenic hearts. These results demonstrate that Akt phosphorylation during I/R is modulated by IGF-1 and prevents apoptosis in hearts that overexpress the IGF-1 transgene.
Androstadienes↗
Canine ventricular myocytes possess a renin-angiotensin system that is upregulated with heart failure.
Ventricular pacing leads to a dilated myopathy in which cell death and myocyte hypertrophy predominate. Because angiotensin II (Ang II) stimulates myocyte growth and triggers apoptosis, we tested whether canine myocytes express the components of the renin-angiotensin system (RAS) and whether the local RAS is upregulated with heart failure. p53 modulates transcription of angiotensinogen (Aogen) and AT(1) receptors in myocytes, raising the possibility that enhanced p53 function in the decompensated heart potentiates Ang II synthesis and Ang II-mediated responses. Therefore, the presence of mRNA transcripts for Aogen, renin, angiotensin-converting enzyme, chymase, and AT(1) and AT(2) receptors was evaluated by reverse transcriptase-polymerase chain reaction in myocytes. Changes in the protein expression of these genes were then determined by Western blot in myocytes from control dogs and dogs affected by congestive heart failure. p53 binding to the promoter of Aogen and AT(1) receptor was also determined. Ang II in myocytes was measured by ELISA and by immunocytochemistry and confocal microscopy. Myocytes expressed mRNAs for all the constituents of RAS, and heart failure was characterized by increased p53 DNA binding to Aogen and AT(1). Additionally, protein levels of Aogen, renin, cathepsin D, angiotensin-converting enzyme, and AT(1) were markedly increased in paced myocytes. Conversely, chymase and AT(2) proteins were not altered. Ang II quantity and labeling of myocytes increased significantly with cardiac decompensation. In conclusion, dog myocytes synthesize Ang II, and activation of p53 function with ventricular pacing upregulates the myocyte RAS and the generation and secretion of Ang II. Ang II may promote myocyte growth and death, contributing to the development of heart failure.
Actins↗
Transplanted adult bone marrow cells repair myocardial infarcts in mice.
Occlusion of the anterior descending left coronary artery leads to ischemia, infarction, and loss of function in the left ventricle. We have studied the repair of infarcted myocardium in mice using highly enriched stem/progenitor cells from adult bone marrow. The left coronary artery was ligated and 5 hours later Lin- c-kit+ bone marrow cells obtained from transgenic male mice expressing enhanced green fluorescent protein (EGFP) were injected into the healthy myocardium adjacent to the site of the infarct. After 9 days the damaged hearts were examined for regenerating myocardium. A band of new myocardium was observed in 12 surviving mice. The developing myocytes were small and resembled fetal and neonatal myocytes. They were positive for EGFP, Y chromosome, and several myocyte-specific proteins including cardiac myosin, and the transcription factors GATA-4, MEF2, and Csx/Nkx2.5. The cells were also positive for connexin 43, a gap junction/intercalated disc component indicating the onset of intercellular communication. Myocyte proliferation was demonstrated by incorporation of BrdU into the DNA of dividing cells and by the presence of the cell cycle-associated protein K167 in their nuclei. Neo-vascularization was also observed in regenerating myocardium. Endothelial and smooth muscle cells in developing capillaries and small arterioles were EGFP-positive. These cells were positive for Factor VIII and alpha smooth muscle actin, respectively. No myocardial regeneration was observed in damaged hearts transplanted with Lin- c-kit- bone marrow cells, which lack bone marrow-regenerating activity. Functional competence of the repaired left ventricle was improved for several hemodynamic parameters. These in vivo findings demonstrate the capacity of highly enriched Lin- c-kit+ adult bone marrow cells to acutely regenerate functional myocardium within an infarcted region.
Actins↗
Hyperglycemia activates p53 and p53-regulated genes leading to myocyte cell death.
To determine whether enzymatic p53 glycosylation leads to angiotensin II formation followed by p53 phosphorylation, prolonged activation of the renin-angiotensin system, and apoptosis, ventricular myocytes were exposed to levels of glucose mimicking diabetic hyperglycemia. At a high glucose concentration, O-glycosylation of p53 occurred between 10 and 20 min, reached its peak at 1 h, and then decreased with time. Angiotensin II synthesis increased at 45 min and 1 h, resulting in p38 mitogen-activated protein (MAP) kinase-driven p53 phosphorylation at Ser 390. p53 phosphorylation was absent at the early time points, becoming evident at 1 h, and increasing progressively from 3 h to 4 days. Phosphorylated p53 at Ser 18 and activated c-Jun NH(2)-terminal kinases were identified with hyperglycemia, whereas extracellular signal-regulated kinase was not phosphorylated. Upregulation of p53 was associated with an accumulation of angiotensinogen and AT(1) and enhanced production of angiotensin II. Bax quantity also increased. These multiple adaptations paralleled the concentrations of glucose in the medium and the duration of the culture. Myocyte death by apoptosis directly correlated with glucose and angiotensin II levels. Inhibition of O-glycosylation prevented the initial synthesis of angiotensin II, p53, and p38-MAP kinase (MAPK) phosphorylation and apoptosis. AT(1) blockade had no influence on O-glycosylation of p53, but it interfered with p53 phosphorylation; losartan also prevented phosphorylation of p38-MAPK by angiotensin II. Inhibition of p38-MAPK mimicked at a more distal level the consequences of losartan. In conclusion, these in vitro results support the notion that hyperglycemia with diabetes promotes myocyte apoptosis mediated by activation of p53 and effector responses involving the local renin-angiotensin system.
Angiotensin II↗
IGF-1 overexpression inhibits the development of diabetic cardiomyopathy and angiotensin II-mediated oxidative stress.
Stimulation of the local renin-angiotensin system and apoptosis characterize the diabetic heart. Because IGF-1 reduces angiotensin (Ang) II and apoptosis, we tested whether streptozotocin-induced diabetic cardiomyopathy was attenuated in IGF-1 transgenic mice (TGM). Diabetes progressively depressed ventricular performance in wild-type mice (WTM) but had no hemodynamic effect on TGM. Myocyte apoptosis measured at 7 and 30 days after the onset of diabetes was twofold higher in WTM than in TGM. Myocyte necrosis was apparent only at 30 days and was more severe in WTM. Diabetic nontransgenic mice lost 24% of their ventricular myocytes and showed a 28% myocyte hypertrophy; both phenomena were prevented by IGF-1. In diabetic WTM, p53 was increased in myocytes, and this activation of p53 was characterized by upregulation of Bax, angiotensinogen, Ang type 1 (AT(1)) receptors, and Ang II. IGF-1 overexpression decreased these biochemical responses. In vivo accumulation of the reactive O(2) product nitrotyrosine and the in vitro formation of H(2)O(2)-(.)OH in myocytes were higher in diabetic WTM than TGM. Apoptosis in vitro was detected in myocytes exhibiting high H(2)O(2)-(.)OH fluorescence, and apoptosis in vivo was linked to the presence of nitrotyrosine. H(2)O(2)-(.)OH generation and myocyte apoptosis in vitro were inhibited by the AT(1) blocker losartan and the O(2) scavenger TIRON: In conclusion, IGF-1 interferes with the development of diabetic myopathy by attenuating p53 function and Ang II production and thus AT(1) activation. This latter event might be responsible for the decrease in oxidative stress and myocyte death by IGF-1.
Angiotensin II↗
Myocyte death and myocyte regeneration in the failing human heart.
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Animals↗
Myocardial cell death in human diabetes.
The renin-angiotensin system is upregulated with diabetes, and this may contribute to the development of a dilated myopathy. Angiotensin II (Ang II) locally may lead to oxidative damage, activating cardiac cell death. Moreover, diabetes and hypertension could synergistically impair myocardial structure and function. Therefore, apoptosis and necrosis were measured in ventricular myocardial biopsies obtained from diabetic and diabetic-hypertensive patients. Accumulation of a marker of oxidative stress, nitrotyrosine, and Ang II labeling were evaluated quantitatively. The diabetic heart showed cardiac hypertrophy, cavitary dilation, and depressed ventricular performance. These alterations were more severe with diabetes and hypertension. Diabetes was characterized by an 85-fold, 61-fold, and 26-fold increase in apoptosis of myocytes, endothelial cells, and fibroblasts, respectively. Apoptosis in cardiac cells did not increase additionally with diabetes and hypertension. Diabetes increased necrosis by 4-fold in myocytes, 9-fold in endothelial cells, and 6-fold in fibroblasts. However, diabetes and hypertension increased necrosis by 7-fold in myocytes and 18-fold in endothelial cells. Similarly, Ang II labeling in myocytes and endothelial cells increased more with diabetes and hypertension than with diabetes alone. Nitrotyrosine localization in cardiac cells followed a comparable pattern. In spite of the difference in the number of nitrotyrosine-positive cells with diabetes and with diabetes and hypertension, apoptosis and necrosis of myocytes, endothelial cells, and fibroblasts were detected only in cells containing this modified amino acid. In conclusion, local increases in Ang II with diabetes and with diabetes and hypertension may enhance oxidative damage, activating cardiac cell apoptosis and necrosis.
Angiotensin II↗
Adenovirus-mediated VEGF(121) gene transfer stimulates angiogenesis in normoperfused skeletal muscle and preserves tissue perfusion after induction of ischemia.
BACKGROUND: Administration of angiogenic factors stimulates neovascularization in ischemic tissues. However, there is no evidence that angiogenesis can be induced in normoperfused skeletal muscles. We tested the hypothesis that adenovirus-mediated intramuscular (IM) gene transfer of the 121-amino-acid form of vascular endothelial growth factor (AdCMV.VEGF(121)) could stimulate neovascularization in nonischemic skeletal muscle and consequently attenuate the hemodynamic deficit secondary to surgically induced ischemia. METHODS AND RESULTS: Rabbits and rats received IM injections of AdCMV.VEGF(121), AdCMV.Null, or saline in the thigh, 4 weeks (rabbits) or 2 weeks (rats) before femoral artery removal in the injected limb. In unoperated rats, at the site of injection of AdCMV.VEGF(121), we found 96% and 29% increases in length density of arterioles and capillaries, respectively. Increased tissue perfusion (TP) to the ischemic limb in the AdCMV.VEGF(121) group was documented, as early as day 1 after surgery, by improved blood flow to the ischemic gastrocnemius muscle measured by radioactive microspheres (AdCMV.VEGF(121)=5.69+/-0.40, AdCMV.Null=2.97+/-0.50, and saline=2.78+/-0.43 mL x min(-1) x 100 g(-1), P<0.001), more angiographically recognizable collateral vessels (angioscore) (AdCMV. VEGF(121)=50.58+/-1.48, AdCMV.Null=29.08+/-4.22, saline=11.83+/-1.90, P<0.0001), and improvement of the bioenergetic reserve of the gastrocnemius muscle as assessed by (31)P NMR spectroscopy. Follow-up studies showed that superior TP to the ischemic limb in the AdCMV.VEGF(121) group persisted until it was equalized by spontaneous collateral vessel development in untreated animals. CONCLUSIONS: IM administration of AdCMV.VEGF(121) stimulates angiogenesis in normoperfused skeletal muscles, and the newly formed vessels preserve TP after induction of ischemia.
Adenoviridae↗
Myocyte death in the pathological heart.
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Cardiomyopathies↗
Telomerase activity in rat cardiac myocytes is age and gender dependent.
Telomerase replaces telomeric repeat DNA lost during the cell cycle, restoring telomere length. This enzyme is present only during cell replication and its activity reflects the extent of proliferation. Whether cardiac myocytes are terminally differentiated cells is still a highly controversial issue, and the possibility of myocyte division is frequently rejected. On this basis, telomerase was measured in pure preparations of myocytes, isolated from rats throughout their lifespan. Fetal and neonatal rat myocytes were used as positive control cells. Contrary to expectation, the authors report that telomerase activity was detectable in pure preparations of young adult, fully mature adult, and senescent ventricular myocytes, defeating the dogma that this cell population is permanent and irreplaceable. Aging decreased 31% telomerase activity in male myocytes. An opposite effect occurred in female myocytes in which this enzyme increased 72%. This differential adaptation between the two genders in the rat model may be relevant to observations in humans; myocyte loss occurs in men as a function of age, whereas myocyte number is preserved in women. The greater growth potential of female myocytes may be critical for the longer lifespan and decreased incidence of heart failure in women.
Aging↗