Abstract 12266: CCND2 Modified mRNA Activates the Cell Cycle in Cardiomyocytes and Improves Recovery From Myocardial Infarction in Small and Large Mammals

Abstract

Background: Experiments in mammalian models of cardiac injury suggest that the cardiomyocyte (CM)-specific overexpression of cyclin D2 (CCND2 in humans) improves recovery from myocardial infarction (MI). The primary objective of this investigation was to demonstrate that our Specific Modified mRNA Translation System (SMRTs) can induce CCND2 expression in CMs (CCND2-CMs) and replicate the benefits observed in other studies of CM-specific CCND2 overexpression for myocardial repair. Methods: The CCND2-CM SMRTs consists of two modRNA constructs: one codes for CCND2 and contains a binding site for L7Ae, and the other codes for L7Ae and contains recognition elements for the CM-specific microRNAs miR-1 and miR-208. Thus, L7Ae suppresses CCND2 translation in noncardiomyocytes but is itself suppressed by endogenous miR-1 and -208 in CMs, thereby facilitating CM-specific CCND2 expression. Experiments were conducted in both mouse and pig models of MI, and control assessments were performed in animals treated with an SMRTs coding for the CM-specific expression of luciferase or GFP, in animals treated with L7Ae modRNA alone or with the delivery vehicle, and in Sham-operated animals. Results: CCND2 was abundantly expressed in cultured, post-mitotic CMs two days after transfection with CCND2-CM SMRTs, and the increase was accompanied by the upregulation of markers for cell-cycle activation and proliferation (e.g., Ki67 and Aurora B kinase). When the GFP-CM SMRTs was intramyocardially injected into infarcted mouse hearts, the GFP signal was observed in CMs but no other cell type. In both the mouse and pig MI models, CM proliferation (on Day 7 and Day 3 after treatment administration in mice and pigs, respectively) was significantly greater, left-ventricular ejection fractions (Days 7 and 28 in mice, Days 10 and 28 in pigs) were significantly higher, and infarcts (Day 28 in both species) were significantly smaller in animals treated with CCND2-CM SMRTs than in any other group that underwent MI induction. Conclusion: Intramyocardial injections of the CCND2-CM SMRTs promoted CM proliferation, reduced infarct size, and improved cardiac performance in small and large mammalian hearts with AMI.