Abstract 333: Cardiomyocyte Death and Fibrotic Scarring in the Infarcted Neonatal Mouse Heart

As one the leading causes of death in the United States, myocardial infarction (MI) occurs every 40 seconds, causing severe public health burden. Following MI, the loss of healthy cardiomyocytes leads to decreased contractility and eventually heart failure. Mature mammalian cardiomyocytes have a low turnover rate at only 0.5-2% per year, insufficient for repopulating damaged myocardium after MI. However, a contradictory discovery was made showing that the neonatal mammalian heart is regenerative, although this reparative ability is lost within days after birth. A great amount of effort is needed to understand the mechanisms underlying neonatal cardiomyocyte regeneration. In the current project, we attempt to profile different types of cell death in regenerating and non-regenerating mouse models following MI, in order to gain insights into a favorable type of cardiomyocyte death during regeneration. We induced MI in postnatal day 1 (P1, regenerative), and postnatal day 7 (P7, non-regenerative) mouse hearts by left anterior descending artery occlusion (LAD-O). The progressive scar formation was assessed using Masson’s Trichrome staining at multiple timepoints up to 14 days after MI. At each time point, we profile three major types of regulated cell death, apoptosis, necroptosis, and ferroptosis, using immunofluorescence staining. We also used AC16, a human cardiomyocyte cell line, to investigate the role of cell density in the regulation of ferroptosis. We found that the scar formation was most dynamic between 2 and 3 days after MI and that the course of scar formation varied greatly between P1 and P7 hearts. Immunofluorescence of different cell death markers reveal differentially progressed cell death between P1 and P7 hearts after MI. Our results indicate a different pattern of cardiomyocyte death in the regenerative P1 heart compared to the non-regenerative P7 heart, that could be more favorable for myocardial regeneration.