Abstract-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 p16 INK4a , and apoptosis of CPCs, impairing the growth reserve of the heart. However, ablation of the p66 shc 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 p66shcϪ/Ϫ , whereas CPC apoptosis and myocyte apoptosis and necrosis prevail in diabetic wild type. Expansion of CPCs and developing myocytes preserves cardiac function in diabetic p66shcϪ/Ϫ , 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. Key Words: cardiac stem cells Ⅲ myocyte regeneration Ⅲ replicative senescence Ⅲ telomeric shortening D eath of cardiac cells with chronic loss of myocytes and vascular structures has been proposed as the underlying cause of the anatomical and functional alterations of the diabetic heart. 1 However, myocyte death and defects in the mechanical behavior, regulatory proteins, and Ca 2ϩ cycling of myocytes with diabetes have left unanswered the question of whether these variables play a primary role in the onset of the myopathy or represent secondary events related to the progression of the cardiac disease. Similar abnormalities occur with myocyte hypertrophy associated with ischemic and nonischemic cardiomyopathy, and myocyte death is commonly found in the failing heart. Accumulating evidence supports the notion that the heart possesses a compartment of multipotent progenitor cells (CPCs) that differentiate into myocytes, endothelial cells, and smooth muscle cells in vitro 2-4 and in vivo. 2 The heart constantly renews itself and an imbalance between cell death and regeneration may be present with diabetes and could be mediated by defects in growth and survival of CPCs.Hyperglycemia leads to enzymatic O-glycosylation of proteins, including the transcription factor p53, whose activation upregulates the local renin-angiotensin system and the synthesis of angiotensin II (Ang II)...

The possibility that adult bone marrow cells (BMCs) retain a remarkable degree of developmental plasticity and acquire the cardiomyocyte lineage after infarction has been challenged, and the notion of BMC transdifferentiation has been questioned. The center of the controversy is the lack of unequivocal evidence in favor of myocardial regeneration by the injection of BMCs in the infarcted heart. Because of the interest in cell-based therapy for heart failure, several approaches including gene reporter assay, genetic tagging, cell genotyping, PCR-based detection of donor genes, and direct immunofluorescence with quantum dots were used to prove or disprove BMC transdifferentiation. Our results indicate that BMCs engraft, survive, and grow within the spared myocardium after infarction by forming junctional complexes with resident myocytes. BMCs and myocytes express at their interface connexin 43 and N-cadherin, and this interaction may be critical for BMCs to adopt the cardiomyogenic fate. With time, a large number of myocytes and coronary vessels are generated. Myocytes show a diploid DNA content and carry, at most, two sex chromosomes. Old and new myocytes show synchronicity in calcium transients, providing strong evidence in favor of the functional coupling of these two cell populations. Thus, BMCs transdifferentiate and acquire the cardiomyogenic and vascular phenotypes restoring the infarcted heart. Together, our studies reveal that locally delivered BMCs generate de novo myocardium composed of integrated cardiomyocytes and coronary vessels. This process occurs independently of cell fusion and ameliorates structurally and functionally the outcome of the heart after infarction. myocardial infarction ͉ myocardial regeneration ͉ stem cells ͉ transdifferentiation T o date, the hematopoietic stem cell appears to be the most versatile stem cell in crossing lineage boundaries and the most prone to break the law of tissue fidelity (1). Early studies on c-kit-positive bone marrow cell (BMC) differentiation into myocardium have generated great enthusiasm (2, 3), but other observations have rejected the initial results (4-6) and promoted a wave of skepticism about the therapeutic potential of BMCs for the injured heart. The major criticisms include: (i) lack of utilization of genetic markers for the recognition of donor BMCs and their progeny; (ii) inaccurate interpretation of the original data due to autofluorescence artifacts; and (iii) the possibility that myocyte regeneration is mediated by fusion of BMCs with resident myocytes rather than BMC transdifferentiation. To address these important questions and demonstrate reproducibility of results, four laboratories with complementary expertise have undertaken a series of joined experiments to acquire information on the plasticity of BMCs and their therapeutic potential for the infarcted heart.In this effort, BMCs for myocardial regeneration were obtained from three transgenic mice. In the first, EGFP was driven by the ubiquitous ␤-actin promoter; in the second, EGFP was ...

Ischemic heart disease is characterized chronically by a healed infarct, foci of myocardial scarring, cavitary dilation, and impaired ventricular performance. These alterations can only be reversed by replacement of scarred tissue with functionally competent myocardium. We tested whether cardiac progenitor cells (CPCs) implanted in proximity of healed infarcts or resident CPCs stimulated locally by hepatocyte growth factor and insulin-like growth factor-1 invade the scarred myocardium and generate myocytes and coronary vessels improving the hemodynamics of the infarcted heart. Hepatocyte growth factor is a powerful chemoattractant of CPCs, and insulin-like growth factor-1 promotes their proliferation and survival. Injection of CPCs or growth factors led to the replacement of approximately 42% of the scar with newly formed myocardium, attenuated ventricular dilation and prevented the chronic decline in function of the infarcted heart. Cardiac repair was mediated by the ability of CPCs to synthesize matrix metalloproteinases that degraded collagen proteins, forming tunnels within the fibrotic tissue during their migration across the scarred myocardium. New myocytes had a 2n karyotype and possessed 2 sex chromosomes, excluding cell fusion. Clinically, CPCs represent an ideal candidate cell for cardiac repair in patients with chronic heart failure. CPCs may be isolated from myocardial biopsies and, following their expansion in vitro, administered back to the same patients avoiding the adverse effects associated with the use of nonautologous cells. Alternatively, growth factors may be delivered locally to stimulate resident CPCs and promote myocardial regeneration. These forms of treatments could be repeated over time to reduce progressively tissue scarring and expand the working myocardium.