Abstract 127: Mode of Injury Affects the Course of Regeneration and Repair in Neonatal and Adult Mouse Heart
PURPOSE: Recent reports have demonstrated complete cardiac regeneration in newborn mice following resection of the cardiac apex. However, different types of injury could affect the mechanism of regeneration and repair.
HYPOTHESIS: We aimed to test the hypothesis that the course of repair and regeneration after MI is different from apical resection in both neonatal and adult mouse heart.
Methods and Results: Apical resection or permanent LAD coronary artery ligation was induced in 1-day-old or 12-week-old ICR mice. Echocardiography was used to confirm and monitor cardiac injury and remodeling. Mice were euthanized at different time points after operation, and hearts were harvested, processed, immunostained and compared with sham operated neonatal and adult hearts. Histological and immunohistochemical examination of both resected and infarcted neonatal hearts revealed inflammation and granulation tissue formation within 3 to 5 days. In the resected hearts, early regeneration was identified at the injured sites, and marked dedifferentiation of cardiomyocytes, represented by sarcomeric disassembly and marginalization, was evident around the injured areas. In addition, we noticed intensive proliferation of young cardiomyocytes which infiltrated the granulation tissue and formed a new myocardium within 21 days. In contrast, incomplete regeneration with residual small infract was detected 28 days after coronary occlusion. Echocardiography at 2,7,14 and 28 days after MI confirmed deteriorating LV function and LV remodeling with apical aneurysm formation. Surprisingly, 21 days after cardiac injury in adult mice, MI produced typical, thin, fibrotic scar whereas apical resection produced an apical tumor-like thick scar.
Conclusions: The mode of injury, whether resection or infarction, affect regeneration and repair in both neonatal and adult mouse heart. Particularly, after apical resection, the newborn heart almost completely regenerates whereas regeneration is incomplete after MI, suggesting that infarction and subsequent inflammation might inhibit complete regeneration. Understanding these differences could be translated to development of new approaches to induce myocardial regeneration in adult heart.
- © 2013 by American Heart Association, Inc.