Abstract 245: Cardiac Stem Cells and Myocyte Regeneration in Diabetic Cardiomyopathy

Abstract

The mammalian heart contains a pool of resident c-kit-positive cardiac stem cells (CSCs), raising questions concerning their role in the etiology of the diabetic myopathy. The objective of the current study was to determine whether the negative effects of diabetes on the adult heart are dictated by defects in CSC growth and lineage commitment. Type I insulin-dependent diabetes mellitus was induced in mice by streptozotocin administration. The kinetics of CSCs and cardiomyocytes was measured 3, 7, 10, 20, and 30 days after the onset of diabetes, by implementing a hierarchically structured cell system, which allows the quantitative analysis of the rate of cell turnover. The multiple variables required to apply this mathematical model were measured by confocal microscopy. They included first the number of CSCs, LCCs (lineage committed cells: myocyte progenitors-precursors), transit amplifying myocytes, and post-mitotic myocytes in the left ventricular (LV) myocardium. Additionally, the fraction of cycling CSCs and the length of their cell cycle were measured, together with the number of cardiomyocytes dying by apoptosis and necrosis. The specificity of labeling was documented by spectral analysis. The diabetic heart was characterized by a severe time-dependent loss in LV post-mitotic myocytes, dictated primarily by a defect in cell renewal. Under control conditions, 20% of myocytes were replaced per month in the adult mouse heart through activation, cell cycle reentry, and differentiation of CSCs. This value decreased sharply to 6%, 1.4%, 0.5%, 0.07%, and 0.05% at 3, 7, 10, 20 and 30 days after the administration of streptozotocin. The myocardium showed a progressive increase in old cardiomyocytes expressing the senescence-associated protein p16INK4a and p53. Importantly, the severe impairment in myocyte regeneration was coupled with an increase in LV end-diastolic pressure, and a decrease in LV systolic pressure, LV developed pressure, positive and negative dP/dt. Thus, our data indicate that the diabetic myopathy has to be viewed as a stem cell disease in which the decrease in the number of myocytes is a secondary event, resulting from defects in replication and lineage specification of cardiac stem cells.