The Next Regeneration: Identifying Cardiac Regeneration–Inducing MicroRNAs Using Functional Screening

Abstract

As medical and interventional therapies improve, more patients are surviving myocardial infarction. As a consequence, the prevalence of patients surviving with compromised cardiac function is increasing, leading to significant morbidity and mortality. Unlike most organs in the body, it has long been accepted that the myocardium cannot regenerate in the adult because cardiomyocyte proliferation rapidly ceases after birth. Although this prevailing view has gradually given way to one that cardiomyocytes do have a modest capacity for regeneration, the factors that regulate these cells from entering the cell cycle have remained elusive. Eulalio et al hypothesized that microRNAs (miRNAs) serve as molecular regulators that maintain cardiomyocytes in quiescence and that manipulation of these regulators could improve cardiac regeneration and thus function. The investigators used an unbiased functional screening approach for miRNAs able to induce reentry of cardiomyocytes into the cell cycle. Cultures of neonatal rat cardiomyocytes were transfected with a whole-genome miRNA library of 875 mimics and stained for proliferative markers Ki67 and 5-ethynyl-29-deoxyuridine (EdU) and cardiomyocyte marker α-actinin, followed by high-throughput microscopy. miRNAs that increased neonatal rat cardiomyocyte proliferation 2-fold were selected and then also tested in the mouse. The investigators next selected miRNAs to test in postnatal cardiomyocytes isolated from 7-day-old …