Bmi1(+) cardiac progenitor cells contribute to myocardial repair following acute injury

Abstract

Background: The inability of the adult mammalian heart to replace cells lost after severe cardiac injury compromises organ function. Although the heart is one of the least regenerative organs in the body, evidence accumulated in recent decades indicates a certain degree of renewal after injury. We have evaluated the role of cardiac Bmi1(+) progenitor cells (Bmi1-CPC) following acute myocardial infarction (AMI). Methods: Bmi1(Cre/+); Rosa26(YFP/+) (Bmi1-YFP) mice were used for lineage tracing strategy. After tamoxifen (TM) induction, yellow fluorescent protein (YFP) is expressed under the control of Rosa26 regulatory sequences in Bmi1(+) cells. YFP+ cells were tracked following myocardial infarction. Additionally, whole transcriptome analysis of isolated YFP+ cells was performed in unchallenged hearts and after myocardial infarction. Results: Deep-sequencing analysis of Bmi1-CPC from unchallenged hearts suggests that this population expresses high levels of pluripotency markers. Conversely, transcriptome evaluation of Bmi1-CPC following AMI shows a rich representation of genes related to cell proliferation, movement, and cell cycle. Lineage-tracing studies after cardiac infarction show that the progeny of Bmi1-expressing cells contribute to de novo cardiomyocytes (CM) (13.8 +/- 5 \% new YFP+ CM compared to 4.7 +/- 0.9 \% in age-paired non-infarcted hearts). However, apical resection of TM-induced day 1 Bmi1-YFP pups indicated a very minor contribution of Bmi1-derived cells to de novo CM. Conclusions: Cardiac Bmi1 progenitor cells respond to cardiac injury, contributing to the generation of de novo CM in the adult mouse heart.