Adult cardiomyocytes (CMs) are specialized to forcefully contract and relax billions of times during an animal's lifetime. A number of adaptations allow adult CMs to fulfill this role, including: large, elongated shape; highly organized network of cell-cell junctions; reliance on oxidative metabolism; nearly crystalline array of sarcomeres; characteristic organization of calcium release units around a network of plasma membrane invaginations known as T-tubules; cell cycle exit; and expression of adult CM-specific contractile, calcium handling, and ion channel genes. In mouse, most of these adaptations are acquired in the first three postnatal weeks. Little is known about the molecular regulation of the CM maturation program. This information gap limits development of rational approaches to stimulate maturation of stem-cell derived CMs. Furthermore, it is likely that congenital heart disease mutations or abnormal cardiac stress caused by congenital heart malformations impact CM maturation, with implications for long term myocardial performance of congenital heart disease patients. Our long term goal is to understand the regulatory program that governs CM maturation. Our preliminary data show that GATA4 and GATA6 (GATA4/6) transcription factors are essential for CM maturation. In addition, a forward genetic screen uncovered TAF3, a component of the RNA Polymerase II pre-initiation complex and a reader of H3K4me3 epigenetic marks, as a novel maturation regulators. Using a number of unique and novel tools and approaches, this proposal will investigate mechanisms that control CM maturation.
Aim 1 will dissect the mechanisms by which GATA4 and GATA6 regulate enhancer activity during CM maturation.
Aim 2 will further characterize TAF3 mutants and dissect the mechanisms by which it regulates maturation.
Aim 3 will apply our innovative in vivo forward genetic screen to discover signaling molecules and congenital heart disease genes that are essential for CM maturation. The coordinated transformation of fetal CMs to their mature counterparts is among the least well understood aspects of cardiac development. Success with this proposal's aims will advance our knowledge in this unexplored frontier of cardiac development.

Public Health Relevance

Mature heart muscle cells (cardiomyocytes) acquire many specialized features that enable them to pump strongly and efficiently over an entire human lifetime. These features are not present in fetal cardiomyocytes. There is little known about the program that regulates this process of cardiomyocyte maturation. The goal of this project is to understand the regulatory mechanisms that control cardiomyocyte maturation. This knowledge would enhance efforts at regenerating the heart and developing new therapies for heart disease and failure.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Cardiovascular Differentiation and Development Study Section (CDD)
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Li, Huiqing
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Boston Children's Hospital
United States
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