Molecular Control of Cardiac Fetal/Neonatal Remodeling

Down-regulation of MEIS1 promotes the maturation of oxidative phosphorylation in perinatal cardiomyocytes

Fetal cardiomyocytes shift from glycolysis to oxidative phosphorylation around the time of birth. Myeloid ecotropic viral integration site 1 (MEIS1) is a transcription factor that promotes glycolysis in hematopoietic stem cells. We reasoned that MEIS1 could have a similar role in the developing heart. We hypothesized that suppression of MEIS1 expression in fetal sheep cardiomyocytes leads to a metabolic switch as found at birth. Expression of MEIS1 was assayed in left ventricular cardiac tissue and primary cultures of cardiomyocytes from fetal (100- and 135-d gestation, term = 145 d), neonatal, and adult sheep. Cultured cells were treated with short interfering RNA (siRNA) to suppress MEIS1. Oxygen consumption rate was assessed with the Seahorse metabolic flux analyzer, and mitochondrial activity was assessed by staining cells with MitoTracker Orange. Cardiomyocyte respiratory capacity increased with advancing age concurrently with decreased expression of MEIS1. MEIS1 suppression with siRNA increased maximal oxygen consumption in fetal cells but not in postnatal cells. Mitochondrial activity was increased and expression of glycolytic genes decreased when MEIS1 expression was suppressed. Thus, we conclude that MEIS1 is a key regulator of cardiomyocyte metabolism and that the normal down-regulation of MEIS1 with age underlies a gradual switch to oxidative metabolism.-Lindgren, I. M., Drake, R. R., Chattergoon, N. N., Thornburg, K. L. Down-regulation of MEIS1 promotes the maturation of oxidative phosphorylation in perinatal cardiomyocytes.

Cardiac regeneration: All work and no repair?

Structural changes in the developing heart may influence the limited regenerative capacity of the adult heart. We examine how the workload exerted on the adult mammalian heart may limit regenerative capability and discuss recent therapies that demonstrate beneficial effects through unloading the heart.

Regulation of Cardiac Cell Fate by microRNAs: Implications for Heart Regeneration

microRNAs are post-transcriptional regulators of gene expression that have been shown to be central players in the establishment of cellular programs, often acting as switches that control the choice between proliferation and differentiation during development and in adult tissues. The heart develops from two small patches of cells in the mesoderm, the heart fields, which originate the different cardiac cell types, including cardiomyocytes, vascular smooth muscle and endothelial cells. These progenitors proliferate and differentiate to establish a highly connected three-dimensional structure, involving a robust succession of gene expression programs strongly influenced by microRNAs. Although the mammalian heart has conventionally been viewed as a post-mitotic organ, cardiac cells have recently been shown to display some regenerative potential, which is nonetheless insufficient to regenerate heart lesions, in contrast with other vertebrates like the zebrafish. Both the proliferation of adult cardiac stem cells and the ability of cardiomyocytes to re-enter the cell cycle have been proposed to sustain these regenerative processes. Here we review the role of microRNAs in the control of stem cell and cardiomyocyte dependent cardiac regeneration processes, and discuss potential applications for the treatment of cardiac injury.