Abstract Body (Do not enter title and authors here): Background: When newborn pigs underwent apical resection (AR) surgery on postnatal day (P) 1, the apex fully regenerated by P28, and when pigs underwent AR on P1 (AR_P1) followed by myocardial infarction (MI) surgery on P28 (AR_P1MI_P28), or MI on P28 without previous AR surgery (MI_P28-only), a large infarct persisted in hearts from the MI_P28-only group on P56, while AR_P1MI_P28 hearts had little evidence of scarring at the same time point, and the improvement appeared to be driven primarily by cardiomyocyte (CM) proliferation. Thus, whereas mammalian CMs normally undergo cell-cycle arrest just a few days after birth, AR_P1 prolonged the duration of CM cell cycle activity and the cells’ proliferative capacity through at least P28.
Hypothesis: The two surgical procedures were performed ~5 mm (AR) and ~20 mm (MI) above the heart base; thus, we hypothesize that AR_P1 preserved the cell-cycle machinery of CMs located throughout the left ventricle (LV), rather than only near the resection site.
Approach: CM single-nucleus RNA sequencing (snRNAseq) data were collected from uninjured (CTL) pigs on P14 (CTL-P14) and from the apex zone (AZ) and remote zone (RZ) of the LV in AR_P1 pig hearts on P2, P4, P8, and P15. These data were integrated with data collected from AR_P1 hearts on P28, from the hearts of CTL pigs on P1, P2, and P28, and from the hearts of fetal pigs (Fetal) in our previous studies, and then the expanded snRNAseq dataset was evaluated with our cell-cycle-specific Autoencoder to identify clusters of cycling CMs, which were defined by the co-enrichment of each of five markers for cell-cycle activity or proliferation (AURKB, MKI67, INCENP, BIRC5, and CDCA8). CM proliferation was also evaluated in AR_P1 hearts on P15 and CTL hearts on P14 via immunohistological analysis of phosphorylated histone 3 (PH3) and symmetric Aurora B (sAUB).
Results: Cycling CMs were significantly more common in Fetal hearts and in both the AZ and the RZ of AR_P1 hearts on P8 and P15 than in CTL hearts on P14. PH3- and sAUB-expressing CMs were also more common in the AZ and RZ of AR_P1 hearts on P15 than in CTL hearts on P14.
Conclusion: AR_P1 preserved the cell-cycle activity and proliferative capacity of CMs throughout the LV.