Control of Cardiomyocyte Proliferation Through p53/Mdm2-Regulated MicroRNAs

Abstract

Heart failure is a leading cause of morbidity and mortality in Canada. As the quality of life and prognosis for these patients is poor, therapies to prevent and treat heart failure are urgently required. Adult cardiomyocytes (CM) are terminally differentiated cells with minimal regenerative capacity, making cardiac tissue particularly vulnerable to injury. Thus, defining the roadblocks responsible for adult CM cell cycle arrest lies at the core of developing regenerative therapies for cardiac diseases. We have previously demonstrated that inactivating the p53/ Mdm2 tumor suppressor circuitry, specifically in the heart, can allow differentiated CMs to regain proliferative capacity, through an upregulation of factors involved in cell cycle re-entry. These factors are repressed in quiescent CMs, in part through the action of microRNAs (miRNAs). Notably, knockout of either p53 or Mdm2 individually was insufficient to promote CM proliferation. Therefore, we hypothesized that inactivation of p53/Mdm2-regulated miRNAs could promote the expression of cell cycle activators and induce proliferation of adult murine CMs. Methods: A screen was performed to identify miRNAs regulated by both p53 and Mdm2. We compared total miRNA expression profiles from cardiac specific p53/Mdm2 double knockout (DKO) mouse hearts with those from cardiac-specific single knockouts (p53KO and Mdm2KO), and wild-type controls, using a miRNA microarray. Results: The screen revealed a profile of 14 uniquely downregulated miRNAs in the "proliferative" DKO hearts versus the control that were not found in either of the single KOs. Of the 14 hits, 11 miRNAs were enriched for mRNA targets involved in cell cycle regulation. Conclusion: Ongoing in vitro studies will determine if knock-down of these miRNAs using antagomirs can upregulate neonatal rat CM proliferation. Ultimately, we aim to inject antagomirs targeting these miRNAs into animals post-myocardial infarction to determine the effect of p53/Mdm2-regulated miRNAs on heart function and CM proliferation in vivo.

Akt3 is a target of miR-29c-3p and serves an important function in the pathogenesis of congenital heart disease

“…microRNAs (miRNAs/miRs) are a type of non-coding single-stranded RNA of ~22 nucleotides in length, which have important regulatory functions within cells (5). In recent years, miRNAs have received increasing attention in the field of heart development (6)(7)(8). We previously identified that miR-29c-3p in serum from patients with CHD, and that its expression was significantly increased in the serum of pregnant women carrying fetuses with CHD compared with in that of normal pregnant women (9).…”