Abstract 16383: Cardiomyocyte Cell-Cycle Re-Entry Potentiated by Cardiosphere-Derived Cell Therapy for Myocardial Infarction in Fate-Mapped Bitransgenic Mice
Background: The mechanisms of cardiac regeneration remain unclear. Here we consider cell-cycle re-entry of preformed cardiomyocytes (CMs) as an alternative to activation and/or recruitment of cardiac stem cells. We investigated the ability of adult mammalian CMs to re-enter the cell cycle in the normal and infarcted heart as well as after therapy with cardiosphere-derived cells (CDCs), using a genetic fate mapping approach.
Methods & Results: In bitransgenic MerCreMer-ZEG mice (α-MHC promoter driving expression of tamoxifen-inducible Cre recombinase), ∼80% of α-SA+ cells were labeled with GFP after 14 days of tamoxifen. Mice were then subjected to: a) sham surgery, b) induction of MI by LAD ligation, and c) induction of MI followed by CDC injection. Mice were pulsed with BrdU daily for 5 weeks and sacrificed at weekly intervals. CMs, isolated by Langendorff enzymatic dissociation, underwent FACS-sorting for GFP (>99.5% GFP+) and subsequent flow-cytometric analysis for BrdU and Ki67 expression (Fig. 1). The normal heart contains a small pool of cycling resident CMs (∼0.08%/week, projecting to a myocyte turnover of 4%/yr), which roughly doubles during the first 3 weeks post-MI (∼0.2%/week). CDC therapy further dramatically upregulates the percentage of cycling CMs (to ∼0.5%/week). Immunocytochemistry of isolated CMs confirmed the flow cytometry results, while tissue immunohistochemistry revealed that cycling CMs were concentrated in the border zone. PCR microarray analysis showed upregulation of several genes associated with cell-cycle progression in CMs post MI, the expression of which was further amplified by CDC therapy.
Conclusions: The adult mouse heart contains a small pool of cycling resident cardiomyocytes. MI induces cardiomyocyte cell-cycle re-entry, which is dramatically amplified following CDC therapy. Induction of CM proliferation represents an important, if not dominant, mechanism of cardiac regeneration in response to cell therapy.
- © 2011 by American Heart Association, Inc.