Newborn apical resection preserves the proliferative capacity of cardiomyocytes located throughout the left ventricle

Background: When pigs underwent apical resection (AR) on postnatal day (P) 1 (ARP1) followed by myocardial infarction (MI) on P28, the hearts had little evidence of scarring; meanwhile, hearts underwent MI on P28 without ARP1 showed large infarcts on P56; and the improvement of ARP1 hearts was driven primarily by cardiomyocyte proliferation. AR and MI were performed ~5 mm (AR) and ~20 mm (MI) above the heart apex; thus, we hypothesize that ARP1 preserved the cardiomyocytes cell-cycle throughout the left ventricle, rather than only near the resection site. Methods: Sections of cardiac tissue were collected from the left ventricle of uninjured pigs and from both the border zone (BZ) of AR and uninjured regions (remote zone, [RZ]) in ARP1 hearts. Cardiomyocyte proliferation was evaluated via immunofluorescence analysis of phosphorylated histone 3 [PH3] and symmetric Aurora B (sAuB). Single nucleus RNA sequencing (snRNAseq) data collected from the hearts of fetal pigs, uninjured pigs, and the BZ and RZ of ARP1 pigs was evaluated via our cell-cycle-specific Autoencoder to identify proliferating cardiomyocytes. Results: Cardiomyocyte PH3 and sAuB expression, and percentage of proliferating cardiomyocytes in snRNA data was significantly more common in both BZ and RZ of ARP1 than uninjured hearts but did not differ significantly between the ARP1-BZ and ARP1-RZ at any time point. Heat shock protein HSPA5 and HSP90B1 were overexpressed at both ARP1-BZ and ARP1-RZ. In AC16 cell, overexpression (and knockdown) of HSPA5-HSP90B1 increased (and decrease) cell-cycle activity. Conclusion: ARP1 preserved proliferative capacity of cardiomyocytes located throughout the left ventricle. On neonatal day 1, apical resection was performed by removing 4-5 mm of tissue from the ventricular apex; then, the sternum was re-approximated, the chest was closed in layers, and air was evacuated from the mediastinum. On postnatal day 2, 4, 8, 15, and 28, the hearts were explanted. Tissue from the border zone (next to the resected apex) and remote zone (>2cm above the apex) were collected and being sent for single-nuclei RNA sequencing data.