A reproducible protocol for neonatal ischemic injury and cardiac regeneration in neonatal mice.

Cardiac regeneration is one of the prime visions in cardiovascular research. The mouse neonatal apical resection and left anterior descending artery (LAD) ligation model introduced novel in vivo mammalian assays to study cardiac regeneration. However, recent reports and editorials discussed and critically questioned the value and technical reproducibility of the mouse neonatal myocardial infarction approach, making it paramount to develop and use a reproducible model system. We established a mouse neonatal myocardial infarction model by visually confirmed ligation of the LAD using microsurgery. TdT-mediated dUTP nick-end labeling (TUNEL) proved reproducible massive myocardial infarctions in a defined region of the apex and anterior wall of neonatal and 7-day-old mice. Whereas hearts ligated on postnatal day 7 displayed chronic injury, cardiac samples ligated immediately after birth always showed complete structural regeneration after long-term follow-up. Cardiac regeneration was observed in all mouse stains (C57BL/6J, ICR, and mixed background C57BL/6JxSv129) tested so far. We present a detailed in vivo protocol to study complex mechanisms of complete cardiac repair following ischemic cardiac damage. Neonatal LAD ligation surgery is feasible, and results in reproducible myocardial infarctions 24 h after ligation, and no structural myocardial defects are detectable following long-term follow-up. We encourage the cardiovascular community to use our protocol and teaching video to answer key scientific questions in the field of cardiac regeneration.