Abstract 3181: Myocardial Injury Induces the Expansion and Cardiomyogenic Differentiation of Postnatal Nkx2.5 Progenitor Cells via Inflammatory Signals
Recent studies have demonstrated the capacity of postnatal mammalian heart to undergo cardiomyocyte renewal; however, evidence is lacking for a direct progenitor cell role in this process. Using an Nkx2.5 enhancer-eGFP transgenic mice that express eGFP in embryonic cardiac precursor cells, we found a declining number of eGFP+ cells in the hearts of postnatal mice up to 6 months after birth. Remarkably, these eGFP+ cells expands 4 – 6 fold at one week following myocardial injury and this expansion was reduced by 72% (p<0.05) when mice were treated with 0.35 mg/mL oral ibuprofen. Global analysis of gene expression revealed that the post-injury eGFP+ cells represent an expanded population of pre-injury eGFP+ cells and do not resemble differentiated cardiomyocytes with reactivation of fetal gene program. To examine the fate of these progenitor cells after injury, we generated a line of inducible Nkx2.5 enhancer-Cre transgenic mice and crossed these mice with the ROSA26-LacZ reporter mice. Lineage tracing of post-infarct progenitor cells reveal that these cells are located initially in the subepicardial space at one week following myocardial infarction and subsequently migrate into the compact myocardium while differentiating into striated cardiomyocytes. The LacZ+ cell area (as a % of total myocardium) increased over time from 0.00±0.0% (mean±SE) at baseline to 0.01±0.011% at 1 week, 0.09±0.51% at 3 weeks, 2.86±0.84% at 6 weeks, and 3.65±1.37% at 12 weeks after injury. To examine the functional requirement of post-injury Nkx2.5 progenitors cells, we used the inducible Nkx2.5 enhancer-Cre mice to conditionally ablate these cells by breeding with ROSA26-diphtheria toxin-A mice. When compared with controls animals, mice with progenitor cell ablation showed greater ventricular dilation and reduced contractility at 6 and 12 weeks following injury (EF mean±SE at 1 week − 0.39±0.021 control vs 0.39±0.027 ablation; 6 weeks − 0.38±0.084 control vs 0.32±0.029 ablation; 12 weeks − 0.38±0.026 control vs 0.31±0.024 ablation). Hence, we provide here the first direct evidence for progenitor cell-mediated cardiomyogenesis in postnatal mammalian heart and the requirement for these cells to support cardiac function following myocardial injury.