Abstract Body (Do not enter title and authors here): Background: The cardiomyocytes (CMs) can not regenerate after myocardial infarction (MI) in adult mammals. FoxM1 is essential for cell proliferation. Targeted deletion of the Foxm1 in mice leads to serious cardiac proliferation defects and embryo death. The primary aim of this study was to demonstrate that the Specific Modified mRNA Translation System (SMRTs) can specifically overexpress FoxM1 in CMs and observe the benefits of overexpressing FoxM1 on myocardial repair in mice and pigs with myocardial injury.

Methods: The FoxM1-CM SMRTs is composed of two modRNA constructs: one encoding L7Ae regulates the specific expression of FoxM1 on the other coding chain in CMs and inhibits its expression in non-cardiomyocytes through he CM-specific microRNAs miR-1 and miR-208 on L7Ae coding chain. Myocardial-specific expression of FoxM1-CM SMRTs and its proliferation-promoting effect were detected in hiPSC-CM (human-induced pluripotent stem cell-derived cardiomyocyte), mouse and pig models (days 3 after FoxM1-CM SMRTs treatment). In vivo experiments were conducted in both mouse and pigs with LAD (left anterior descending) ligation. The effects of FoxM1-CM SMRTs on cardiac function, MI size and hypertrophy in mice and pig models were detected after 4 weeks of FoxM1-CM SMRTs treatment.

Results: FoxM1 was abundantly expressed in postmitotic CMs after transfection with the FoxM1-CM SMRTs, accompanied by activation of cell-cycle and proliferation markers (Ki67, PH3 and Aurora B kinase) and an increase in cell number. When the GFP-CM SMRTs was injected into mouse hearts with MI, GFP was only expressed in CMs, but not in non-CMs. Compared with the MI group, FoxM1-CM SMRTs significantly increased CM proliferation (days 3 after treatment administration in mice and pigs), improved left-ventricular ejection fractions (days 10 and 28 in both species) and hypertrophy, and reduced MI size (days 28 in both species).

Conclusion: Intramyocardial injections of the FoxM1-CM SMRTs promoted CM proliferation, reduced MI size, and improved cardiac function in small and large mammals with acute myocardial infarction.