Epigenetic regulation of the metabolic shift in mammalian perinatal hearts

Abstract: During the transition to extra-uterine life, mammalian hearts undergo a crucial metabolic shift that is essential for neonatal hearts to adapt to normoxic conditions and the increased cardiac workload experienced after birth. Proper metabolic transition is essential for establishing normal heart physiology. The long-term goal of this project is to reveal the molecular and cellular mechanisms that regulate this cardiac metabolic shift using mouse models and ultimately translate our discoveries into clinical applications addressing inborn cardiomyopathies. Mono-ubiquitination of histone H2A K119 (H2AK119Ub) is a major post-translational modification of histone H2A, occurring in 5-15% of total H2A in mammalian cells. H2AK119Ub in the promoter region inhibits RNA polymerase II elongation and acts as a repressive epigenetic mechanism to regulate key developmental programs from drosophila to mammals. The precise level of H2AK119Ub is dynamically controlled by the balance between ubiquitin ligases and deubiquitinases. USP16 is a histone H2AK119Ub-specific deubiquitinase that de- represses gene transcription. To test the role of USP16 in hearts, we specifically deleted Usp16 in the myocardium. All mutant mice died within 3 days after birth and displayed severe myocardial wall anomalies. Our subsequent two-hybrid and biochemical analyses revealed that Nuclear Respiratory Factor 1 (NRF1) is a novel USP16 interaction partner. NRF1 is a nuclear transcription factor that activates expression of the vast majority of nuclear genes encoding subunits of mitochondrial oxidative phosphorylation (OXPHOS) complexes. In support of the functional significance of the USP16-NRF1 interaction, our mRNA-Sequencing analysis revealed that the pathway involved in OXPHOS was most significantly downregulated by myocardial deletion of Usp16. We propose our central hypothesis that USP16 interacts with NRF1 to upregulate expression of nuclear OXPHOS genes, supporting the metabolic shift in perinatal hearts. In Aim 1, we will test how deletion of Usp16 affects the metabolic shift in perinatal hearts. In Aim 2, we will test if OXPHOS genes are major direct regulatory targets of USP16 in perinatal hearts using high-throughput approaches. In Aim 3, we will test the role of NRF1 in loading USP16 onto its target sites. This project will fill a major knowledge gap regarding the basic molecular mechanism underlying the cardiac metabolic shift, which is critical for the proper transition to extra-uterine life. Our research will contribute to the development of novel clinical applications aimed at OXPHOS-associated heart defects.